Clinical Laboratory Data Interpretation (Foundations & System-Specific)

Foundations of Laboratory Data Interpretation

General Principles and Concepts

• Purpose of Laboratory Testing: Laboratory testing is used to detect disease, guide treatment, monitor response to treatment, and monitor disease progression.
• Imperfect Science: Laboratory testing is an imperfect science; it may fail to identify abnormalities (false negatives [FNs]) or identify abnormalities that are not present (false positives [FPs]).
• Clinician’s Role: Clinicians must recognize and understand the terms used to describe laboratory test characteristics and results before applying them to individual patients. Pharmacists must be able to interpret laboratory data for individual patients to practice effectively, as it provides a ‘window’ into a patient’s health and physiological function.
• Comprehensive Assessment: Laboratory data must always be interpreted with reference to the clinical status of the patient and other relevant information. Diagnostic and therapeutic decisions should not be made based on an isolated laboratory report.
• Biomarkers: A biomarker is an objectively measured characteristic that indicates normal biological processes, pathogenic processes, or pharmacologic responses. Glycated hemoglobin A1c (HbA1c) is an example used for long-term glucose control.

Accuracy and Precision

• Accuracy: The extent to which the mean measurement is close to the true value. For a qualitative assay, it’s the sum of true positives (TPs) and true negatives (TNs) divided by the total samples tested.
• Precision: Refers to assay reproducibility, meaning consistent results when the specimen is assayed multiple times. High precision means consistent close agreement of results, but the accuracy of those results is a separate issue. Laboratories are expected to test analytes with accuracy and precision and document quality control.

Types of Laboratory Tests

• Quantitative Tests: Results are reported as an exact numeric measurement (e.g., serum potassium in mEq/L, creatinine clearance in mL/min) and assessed within a reference range.
• Qualitative Tests: Results are reported as either positive or negative without further characterization (e.g., urine pregnancy test).
• Semiquantitative Tests: Provide an estimate of the amount of substance (e.g., urine dipstick tests for protein, pH, specific gravity).
• Screening Tests: Performed in individuals without signs or symptoms to detect disease early, generally inexpensive, quick, and reliable, but require confirmation.
• Diagnostic Tests: Performed on at-risk individuals, typically more expensive, associated with some risk, and provide a definitive answer.

Reference Ranges and Factors Affecting Them

• Reference Range: A numerical range of results likely obtained if the investigation were performed for healthy subjects.
• Interpretation: A result outside a reference range does not always indicate disease, nor does a result within guarantee its absence. Grossly abnormal results usually signify serious problems.
• Factors Affecting Reference Ranges: Age, gender, ethnicity, height, weight, body surface area, pregnancy. For example, plasma volume increases during pregnancy, causing relative hyponatremia and decreased fasting blood glucose.
• Artefact Effects: Results may appear abnormal due to artefact, like factitious elevation of serum potassium from haemolysis of blood samples. Sources of error within the laboratory may also need to be considered.
• Fractions/Subtypes: Some analytes exist in several forms (fractions, subtypes, isoenzymes) each with a different reference range.
• Units: Laboratory results are reported with various units (e.g., mEq/L, mg/dL, mmol/L); lack of standardization can be confusing. The International System of Units (SI) is designated for some measurements but is not universally adopted.

Sensitivity and Specificity

• Sensitivity: The probability that a test result will be positive when disease is present (TP / [TP + FN]).
• Specificity: The probability that a test result will be negative when disease is absent (TN / [TN + FP]). For quantitative tests, it refers to the degree of cross-reactivity with other substances in the sample.
• Test’s Predictive Value: Influenced by the sensitivity and specificity of the test.

Sources of Error and Patient-Specific Factors

• Laboratory Errors: Deteriorated reagents, calibration errors, calculation errors, misreading results, documentation errors, improper sample preparation.
• Patient-Specific Factors:
  • Age: Decreased renal function in elderly, different reference ranges in pediatric patients.
  • Time of Day: Biological rhythms influence hormone levels (e.g., FSH, LH, progesterone).
  • Posture: Affects laboratory results.
  • Disease States: Impact time courses (e.g., post-MI enzyme patterns).
  • Pregnancy: Significant physiological and metabolic changes affect hormone levels, plasma volume, blood glucose, and lipid metabolism.
• Specimen-Related Factors:
  • Specimen Type: Whole blood, plasma, serum, urine, stool, sputum, CSF, tissues. Plasma contains proteins, electrolytes, lipids, carbohydrates, etc.; serum is plasma minus the fibrin clot.
  • Haemolysis: Rupture of red blood cells, which can occur during or after collection, significantly affecting results (e.g., plasma haemoglobin, serum potassium).
  • Improper Handling/Storage: Can compromise specimen integrity and produce unreliable results.

Guidelines for Interpreting Laboratory Results

• Contextual Interpretation: Results must be interpreted in the context of the patient’s clinical status (signs and symptoms). For example, an asymptomatic patient with slightly low potassium causes less concern than a symptomatic patient with similar levels.
• Baseline Results: Establishing a baseline allows identification of early changes, even within the reference range, and sets relative therapeutic goals (e.g., aPTT for heparin anticoagulation).
• Rate of Change and Patterns: Consider the rate of change in values and overall patterns, not just isolated results.
• Spurious Results: Suspect spurious results if values are inconsistent with the patient’s condition; repeat testing may be necessary.

Introduction to Common Laboratory Assays and Technology

Overview of Laboratory Automation and Informatics

• Automation: Many laboratory procedures are now highly automated, especially in chemistry, hematology, and microbial identification. Total Laboratory Automation (TLA) systems aim to improve throughput and real-time analysis.
• Informatics: Large laboratories use informatics to analyze and transmit clinical information efficiently, enhancing healthcare decision-making. Patient access portals provide limited access to results.

Analytical Techniques

Photometry

• Basic Principle: Measurement of absorbance or emittance of light. Many automated chemistry analyzers rely on photometry.
• Spectrophotometry: Measures molecular absorption or emission of light. A spectrophotometer uses a light source, a wavelength selector, a sample container, a detector, and a readout device.
• Densitometry: A specialized form of spectrophotometry used to evaluate electrophoretic patterns after staining.

Electrochemistry

• Basic Principle: Measurement of current or voltage produced by ion activity.
• Potentiometry: Measures electrical potential differences between two electrodes at zero current flow. Widely used for pH, pCO2, and electrolytes in whole blood.

Osmometry

• Principle: Measures total concentration of solute particles in biological fluids (serum, plasma, urine). Based on colligative properties (e.g., freezing-point depression).

Electrophoresis

• Principle: Separates molecules based on their overall molecular charge, shape, and size when exposed to an electric field in a support medium.
• Types: Cellulose acetate, agarose gel, polyacrylamide gel, isoelectric focusing (IEF), two-dimensional (2-D), and capillary electrophoresis (CE).
• Blotting Techniques: Southern (DNA), Northern (RNA), and Western (proteins) blots use electrophoresis followed by probing with labeled molecules to identify specific fragments. Capillary gel electrophoresis (CGE) is used for size-based separation of macromolecules like DNA fragments and proteins.

Chromatography

• Principle: Separates components of a sample based on differences in solubilities or boiling points.
• Gas Chromatography (GC): Used for volatile compounds, where components separate based on boiling points as they pass through a column. Tandem GC/MS systems are common.
• High-Performance Liquid Chromatography (HPLC): Separates non-volatile compounds using a liquid mobile phase. Useful for drugs like indomethacin, cyclosporin.

Immunoassays

• Principle: Utilize immunologically mediated reactions (antigen-antibody binding) to increase sensitivity and specificity. Allow for high sensitivity and specificity.
• Types:
  • Enzyme-Linked Immunosorbent Assay (ELISA): Specific antibody adsorbed to a solid phase; enzyme-labeled antigen competes with unlabeled antigen from sample. Used for serologic tests (e.g., ANA, rheumatoid factor, hepatitis, HIV antigens/antibodies).
  • Enzyme-Multiplied Immunoassay Technique (EMIT):.
  • Fluorescent Polarization Immunoassay (FPIA):.
  • Radioimmunoassay (RIA): Historically significant.
• Applications: Commonly used for therapeutic drug monitoring (e.g., aminoglycosides, vancomycin, digoxin, antiepileptics) and toxicology/drugs of abuse testing.
• Monoclonal Antibodies (moAbs): Development of moAbs has enabled high sensitivity and specificity in immunoassay technology.

Mass Spectrometry (MS)

• Principle: Involves fragmentation and ionization of molecules in the gas phase according to their mass to charge ratio (m/z).
• Gold Standard: Considered the gold standard for the identification of unknown substances, including drugs of abuse.
• Components: Inlet unit, ion source, mass analyzer, ion detector, and data/recording system. Often used in tandem with separation techniques like GC, LC, or CE (e.g., GC/MS).

Cytometry

• Definition: Process of measuring physical, chemical, or other characteristics of cells or biological particles.
• Flow Cytometry: Measures characteristics of thousands of cells per second, distinguishing cell populations based on light scatter and extrinsic properties (e.g., lymphocytes, monocytes, granulocytes; B cells, T cells). Routinely used for classifying leukemia/lymphoma, monitoring HIV/AIDS, and enumerating stem cells.
• Image Cytometry (Histology/Cytology): Analyzes tissue specimens (histology) or individual cells (cytology) using microscopes, cameras, and computers. Applications include measuring DNA content in nuclei for cancer prognosis and detecting nucleic acid sequences for genetic disorders.

Molecular Diagnostics and Genomics

• Molecular Diagnostics: Involves techniques like Polymerase Chain Reaction (PCR) and other nucleic acid amplification techniques to detect specific DNA and RNA sequences, primarily in microbiology and genetic diseases.
• Genomics, Epigenetics, Proteomics: New techniques examining DNA, mRNA, and proteins provide frameworks for molecular classifications and treatments of diseases.
  • Genomics: Genetic analysis (e.g., cystic fibrosis mutations).
  • Proteomics: Study of proteins produced by organisms, impacting medicine as proteins control functional aspects of cells.
  • Bioinformatics: Data derived from array-based comparative genomic hybridization.
• Pharmacogenomics: Field changing rapidly; integrates genetic testing into clinical practice to guide personalized therapies (e.g., warfarin, irinotecan, EGFR mutations in lung cancer). Requires established guidelines and expertise for accurate interpretation.

Nanotechnology

• Emerging Science: Studies interactions of cellular and molecular components at the nanoscale (<100 nm), providing access to cellular and molecular environments. Has potential for simple, inexpensive in vitro and in vivo assessments and for targeting therapies.

Drug Interferences with Test Results

Mechanisms of Interference

• In Vitro Interference: Occurs when drugs in a patient’s body fluid or tissue directly interfere with the analytical process of a laboratory test. This is highly dependent on the methodology; a reaction may occur with one specific assay but not another.
  • Cross-reactivity: Drugs with similar chemical structures can cross-react with assays (e.g., spironolactone, estrogen products, cortisol, or digoxin-like substances with digoxin immunoassays). Fosphenytoin can cross-react with phenytoin in immunoassays.
  • Chelation: A drug chelates with an enzyme activator or reagent used in the in vitro analysis.
  • Absorption at Wavelength: A drug absorbs at the same wavelength as the analyte (e.g., methotrexate interfering with assays using 340–410 nm absorbance range).
  • Other Components: Metabolites can cross-react with parent drugs (e.g., cyclosporine metabolites in HPLC assays), contaminants in herbal products, and inactive ingredients (excipients, preservatives, colorants) can interfere.
  • Specimen Additives: Substances prepackaged in or added to the in vitro system (e.g., lithium heparin interfering with aminoglycoside assays, fluoride causing false increases in BUN).
• In Vivo Interference: The drug’s pharmacological or toxic effects produce specific alterations in laboratory values. This is the cause of most drug-laboratory test interferences.
  • Discoloration of Urine: Drugs can discolor urine, interfering with fluorometric, colorimetric, and photometric tests and masking abnormal urine colors (e.g., amitriptyline turns urine blue-green, phenazopyridine/rifampin turn urine orange-red).
  • False Negatives/Positives: High doses of ascorbic acid (>500 mg/day) can cause false-negative stool occult blood tests. Ampicillin, chloral hydrate, erythromycin can produce urinary fluorescence, interfering with catecholamine tests.

Identifying and Confirming Interferences

• Suspicion: Suspect a drug-laboratory test interference when:
  • An inconsistency appears among clinical, laboratory, and patient-specific information.
  • The results of different tests assessing the same organ function or drug effect conflict.
  • Serial laboratory test values vary greatly over a short period.
• Systematic Process:
  1. Evaluate consistency: Check for inconsistencies among patient’s signs/symptoms, clinical status, and test results.
  2. Rule out other causes: Consider other drugs and diseases.
  3. Dechallenge/Rechallenge: Discontinue the suspected drug and repeat the test to see if dechallenge corrects the abnormality.
  4. Literature Search: Systematically scan tertiary, then secondary, then primary literature to identify and confirm documented interferences.

Resources for Drug Interference Information

• Reference Texts/Databases: Provide foundational content, background material, and current literature (e.g., Young DS. Effects on Clinical Laboratory Tests: Drugs, Disease, Herbs, and Natural Products).
• Drug Information Databases: Include drug information questions and answers; search by drug name or laboratory test. Often provide severity ratings (major/minor) and references to primary literature.
• Local Clinical Laboratory Websites: Convenient for accessing interpretive guides.
• Package Inserts: For immunoassays or commercial assay kits, provide specific guidance on assay performance and known interfering substances.

Point-of-Care Testing (POCT)

Definition and Rationale

• Definition: Laboratory testing performed outside the central laboratory, often near the patient.
• Rationale: Advances in miniaturization of analyzers make POCT an essential and complementary tool for diagnosis and treatment.

Clinical Opportunities and Applications

• Accessibility: Provides rapid turnaround time (results within minutes) and convenient access to test results.
• Settings: Used in private physician offices, group practices, clinics, emergency departments, and increasingly in community pharmacies and ambulatory care clinics.
• Common CLIA-Waived POCTs: Urine pregnancy, urine leukocytes/nitrite, blood glucose, INR, hemoglobin, fecal occult blood, throat swab for Group A streptococci, C-reactive protein, quantitative β-human chorionic gonadotropin, HbA1c, nose/throat swab for influenza, platelet count.
• Chronic Disease Management: Pharmacists performing CLIA-waived POCT can measure analytes like ionized calcium, creatinine, glucose, potassium, sodium, urea nitrogen, hematocrit, liver function enzymes, and albumin. This can assist with medication dosing adjustments for chronic conditions (e.g., diabetes, cardiovascular disease). For diabetes, HbA1c POCTs have improved considerably.
• Infectious Diseases:
  • Influenza: Rapid influenza diagnostic tests (RIDTs) have high specificity but variable sensitivity; useful when influenza prevalence is high.
  • HIV/HCV: POCTs for HIV-1/2 using oral mucosal transudate or whole blood are highly accurate and less technically demanding.
  • Future Applications: Molecular-based CLIA-waived POCTs could enable prompt therapy for sexually transmitted infections (STIs) under protocol.
• Patient Engagement: POCT involves the patient in the laboratory process, providing opportunities for clinicians to give feedback and reinforce risk reduction steps.

Performance Characteristics and Limitations

• Accuracy and Precision: POCT devices are generally not as precise as fully automated central laboratory systems, though imprecision is often an acceptable compromise for rapid turnaround. Analytical performance for HbA1c POCTs has improved.
• Sensitivity and Specificity: Varies with the test type, manufacturer, assay kit, setting, and application. For influenza, RIDTs have high specificity but moderate and variable sensitivity. Oral HIV testing has low sensitivity in acute phase before seroconversion.
• Interference: POCTs use immunoassay techniques, which can have compromises in specificity leading to cross-reactivity (e.g., with amphetamines and opiates), causing preliminary results to be misleading. Lipemia from intravenous lipid emulsion (ILE) therapy can also affect POCT results.
• Sample Type Variability: POCT devices may compare different sample types (e.g., capillary blood from fingerstick vs. venous whole blood), which can explain some variability (e.g., lower lipid values from capillary blood).
• Clinical Interpretation: Requires careful interpretation by pharmacists who are cognizant of proper sample collection technique, timing, and potential for spurious results. POCT is not diagnostic for HIV and requires confirmatory testing.

Resources and Good Laboratory Practices

• Resources: FDA website (list of analytes in waived systems), CMS website (list of waived tests by CPT code), CDC website (professional information, educational resources).
• Good Laboratory Practices:
  • Preanalytical Phase: Ensuring proper sample collection technique and timing, correct identification labels and bar codes, correct tube, and appropriate quality/quantity of material.
  • Analytical Phase: Performing quality control checks, running samples according to manufacturer guidelines.
  • Postanalytical Phase: Issuing test reports, performing supplemental/confirmatory testing, cleaning, disposing biohazard waste, and documenting activities. Pharmacist’s interpretation and communication of results to patient and provider is critical. Reporting to public health agencies may be mandated for certain infectious diseases.

Substance Abuse and Toxicological Tests

General Analytical Techniques

• Immunoassays: Widely available for substances of abuse in hospitals, with results within 1-2 hours. Many POCTs also use immunoassay, providing results in 5-15 minutes.
• Spectrophotometry:.
• Gas Chromatography (GC):.
• High-Performance Liquid Chromatography (HPLC):.
• Atomic Absorption Spectrometry:.
• Mass Spectrometry (MS): The gold standard for identifying unknown substances, including new designer drugs not detectable by routine screens. GC/MS is commonly used for confirmation.

Preliminary and Confirmatory Tests

• Preliminary Tests: Often immunoassays, provide rapid results but due to compromises in specificity, they can have cross-reactivity (especially with amphetamines and opiates).
• Confirmatory Tests: Preliminary immunoassay results cannot stand alone for medicolegal purposes and must be confirmed with more specific analysis (e.g., GC-MS). Confirmation may be routine in some labs or only by physician request, depending on factors like patient care impact, legal actions, and cost.

Interpretation of Results and Interfering Substances

• Negative Result: A negative urine drug screen means the drug was not detected, not necessarily that it was absent or not taken. The drug might not be part of the testing panel (e.g., meperidine/fentanyl not detected on opiate immunoassays).
• Designer Drugs: Illicitly synthesized analogs (designer drugs) are not detected by routine screens because their chemical structure is often unknown, and assays/reference standards are not developed.
• False Positives: Drugs seemingly dissimilar from the target of an immunoassay can cause false-positive results (e.g., naproxen for marijuana/barbiturates, fluoroquinolones for opiates). Ephedrine, pseudoephedrine, and bupropion can cause false positives for amphetamines.
• Interfering Substances: Immunoassay manufacturer’s package insert should be consulted for known interfering substances.
• Reliability Factors: Drug screen reliability and interpretation are affected by drug panel, cutoff values, specimen adulteration, interfering substances, and timing of sample collection.
• Toxicology Hold: Collecting a blood or urine specimen at presentation to the ED but not performing the assay immediately, allowing for later retrospective analysis if needed.

Serum Drug Concentrations in Poisoning and Toxicokinetics

• Objectives of Analysis: Quantitative assays determine the concentration of a substance in a biological specimen, typically serum. Serum is generally not used for drug screening in clinical or workplace settings.
• Usefulness: Serum concentrations for toxins are obtained when the concentration correlates with an effect, outcome, or need for therapy; when the assay is already used for TDM; or for technical ease.
• When to Obtain:
  • To confirm a poisoning diagnosis when in doubt or to aid interpretation of a qualitative urine drug screen.
  • When there is a relationship between serum concentration and toxicity, to assist in patient evaluation or medicolegal purposes.
  • For sustained-release drug ingestions, to indicate peak concentrations and assess decontamination efforts.
  • To determine when to reinitiate drug therapy after toxicity.
  • To guide decisions for risky/expensive therapies like antidotes or special treatments (e.g., hemodialysis).
• Management without Quantitative Analysis: Many poisonings can be managed with exposure history, signs/symptoms, and routine clinical tests (CBC, electrolytes, glucose, INR, LFTs, BUN, creatinine, anion gap, osmolality, ABGs, creatinine kinase).
• Toxicokinetics: The pharmacokinetics of drugs/chemicals in overdose. It’s generally inappropriate to apply pharmacokinetic parameters from therapeutic doses to massive overdoses, as absorption, distribution, metabolism, and elimination can differ.

System-Specific Laboratory Data Interpretation

General Principles for System-Specific Data

• Pharmacist’s Role: A clinical pharmacist must be able to interpret laboratory data as part of an overall clinical assessment to review current drug therapy, suggest drug discontinuation or avoidance (e.g., NSAIDs for renal impairment), identify need for dose adjustment (renal/hepatic dysfunction), guide adequacy of drug response (e.g., blood glucose for insulin), and check for signs of serious drug toxicity (e.g., abnormal biochemical/hematological parameters, elevated LFTs).
• Interpreting Information: This requires a working understanding of frequently used tests and their direct relevance to drug therapy. Accumulating knowledge involves continuously checking reliable reference texts.

Heart: Laboratory Tests and Diagnostic Procedures

• Acute Coronary Syndrome (ACS) Diagnosis:
  • Clinical Presentation: Does not distinguish between unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI).
  • Electrocardiography (ECG): Essential for immediate diagnosis, prognosis, and management options. Differentiates between NSTEMI and STEMI. ECG changes (T-wave inversion, ST-segment depression/elevation, Q-wave) are useful.
  • Biochemical Markers of Myocardial Necrosis: Release of detectable quantities indicates myocardial injury.
    • Cardiac Troponins (cTnI and cTnT): Specific to cardiac cells. Elevated levels define MI in absence of ST-segment elevation. Increased value is ≥99th percentile of a normal population. Probable MI indicated at ≥0.3 ng/mL for cTnI (assay-dependent). High-sensitivity troponin assays are being developed but face challenges with false-positives and standardization.
    • Creatine Kinase (CK) and CK-MB: CK increases about 6 hours post-MI and returns to baseline in 48-72 hours. CK-MB is uncommonly measured now.
  • Other Biochemical Markers in ACS:
    • B-type Natriuretic Peptide (BNP): Neurohormone released by ventricular myocardium in response to volume overload. Strong predictor of short- and long-term mortality in ACS. Levels reduced in obese patients, affecting interpretation.
    • C-reactive Protein (CRP): Non-specific acute-phase reactant, elevated in inflammation. Strong predictor of mortality in ACS, as inflammation plays a role in atherosclerosis and plaque rupture.
• Heart Failure (HF) Diagnosis and Assessment:
  • BNP or NT-proBNP Measurement: Considered the gold standard test for diagnosis and assessment of HF.
  • Left Ventricular Ejection Fraction (LVEF): Essential for differentiating systolic (reduced LVEF) from diastolic (preserved LVEF) HF and targeting therapy.
• Imaging Techniques:
  • Echocardiography: Uses ultrasound to assess cardiac chambers, valves, blood flow, and wall motion.
  • Cardiac Catheterization: Anatomic assessment of heart chambers and coronary arteries.
  • Chest Radiography:.
  • Nuclear Imaging:.

Lipid Disorders

• ASCVD Risk Assessment: A two-part process involving laboratory assessment of the lipid profile and assessment of additional cardiovascular risk factors.
• Lipid Panel (Fasting vs. Nonfasting): Ideally performed fasting (9-12 hours), but nonfasting panels can be considered as TC and HDL cholesterol are unaffected, and LDL/TG changes are less significant than previously thought. A fasting panel is required if TG measurement is the focus or if TGs are >400 mg/dL nonfasting.
• Components of a Lipid Panel:
  • Total Cholesterol (TC):.
  • High-Density Lipoprotein Cholesterol (HDL):.
  • Low-Density Lipoprotein Cholesterol (LDL): Calculated using the Friedewald formula. Desirable <100 mg/dL.
  • Triglycerides (TGs):.
  • Non-HDL Cholesterol: Includes all atherogenic lipoproteins; calculation may not be necessary if LDL and TG are managed.
• Emerging Lipid Risk Factors: Apo B, LDL particle concentration, Lp(a). Apo B is a major component of all atherogenic lipoproteins; higher levels correlate with increased ASCVD risk.
• POCT for Lipids: Devices available for TC, HDL, and TGs, with LDL calculated by the device or user. Useful for screening (e.g., health fairs) but requires follow-up with a provider for complete cardiovascular risk assessment.

Endocrine Disorders

Diabetes Mellitus

• Hyperglycemia Diagnosis: Commonly falls into three categories: diabetes mellitus (DM) or prediabetes, diabetic ketoacidosis (DKA), and hyperosmolar hyperglycemic state (HHS).
• Diagnostic Tools for Hyperglycemia:
  • Glycated Hemoglobin A1c (HbA1c): Reflects long-term glucose control. Used to assess response to therapeutic interventions.
  • Fasting Plasma Glucose (FPG):.
  • Oral Glucose Tolerance Test (OGTT):.
• Glucose Monitoring: Self-monitoring blood glucose (SMBG) is important for adjusting insulin doses and evaluating glucose-lowering agents. Pregnancy requires frequent monitoring (4-6 times/day).
• Diabetic Ketoacidosis (DKA): A urine screen can indicate ketones, but modern assays (nitroprusside-based) primarily detect acetoacetic acid and are less sensitive to β-hydroxybutyric acid, which may predominate in severe hypovolemia or alcoholism.
• Gestational Diabetes Mellitus: Requires frequent blood glucose monitoring.
• Pharmacist’s Role: TDM is used to assess effectiveness of insulin treatment by measuring blood glucose parameters.

Thyroid Disorders

• Thyroid Hormones: Thyroxine (T4), triiodothyronine (T3), and thyroid-stimulating hormone (TSH).
• Hypothalamic-Pituitary-Thyroid Axis: TSH from pituitary stimulates T3/T4 production from thyroid. T3/T4 provide negative feedback to pituitary and hypothalamus.
• Diagnosis:
  • TSH: Most sensitive and specific screening test for primary thyroid dysfunction.
  • Total/Free T4 and T3: Total T3/T4 levels are affected by thyroid-binding globulin (TBG) changes. Free T4/T3 are more accurate but not always measured.
  • Radioactive Iodine Uptake Test: Detects thyroid gland’s ability to trap and concentrate iodine, assessing intrinsic function, but its use is declining.
  • Nonthyroid Laboratory Tests: Hypothyroidism and hyperthyroidism can cause abnormalities in non-thyroid tests (Table 10-7 in source), reflecting widespread effects of thyroid hormones. These support diagnosis when used with specific thyroid function tests and clinical presentation.

Adrenal Disorders

• Adrenal Medulla: Secretes catecholamines (epinephrine, norepinephrine).
• Adrenal Cortex: Secretes hormones (e.g., cortisol, aldosterone, androgens).
• Parameters: (Not detailed in provided text beyond mention of epinephrine/norepinephrine, and corticotropin-releasing hormone, ACTH, cortisol during pregnancy).

The Kidney

• Function: Kidneys maintain homeostasis by excreting water and solutes; also activate/synthesize substances affecting BP, mineral metabolism, RBC production.
• Key Measures of Kidney Function:
  • Glomerular Filtration Rate (GFR): About 125 mL/min (20% of renal plasma flow). Often used as a measure of kidney excretory function.
  • Creatinine Clearance (CrCl): Surrogate marker of renal function, estimated by calculation. Small changes in serum creatinine (SCr) at lower levels represent significant changes in CrCl.
  • Serum Creatinine (SCr): Used in conjunction with CrCl calculation. Influenced by muscle mass, age, gender. Can be falsely elevated by various substances (uric acid, glucose, cefoxitin, flucytosine) in alkaline picrate (Jaffe) assay, or falsely lowered by bilirubin.
  • Blood Urea Nitrogen (BUN): Azotemia refers to elevated BUN (GFR 20–35% of normal); uremia refers to elevated BUN plus other abnormalities (GFR <20–25%). Low BUN can indicate inadequate protein intake or excess intravascular volume.
• Classification of Chronic Kidney Disease (CKD): Based on GFR categories and albuminuria.
• Urinalysis: Semiquantitative tests on urine dipsticks (protein, pH, specific gravity, bilirubin, bile, urobilinogen, blood, hemoglobin, leukocyte esterase, nitrite, glucose, ketones).
  • Proteinuria: Loss of protein in urine (albumin and globulins), characteristic of glomerular disease. Clinical proteinuria >500 mg/day; microalbuminuria 30–300 mg/day. Associated with diabetic nephropathy, glomerular disease, uncontrolled hypertension.
  • Specific Gravity: Correlates with urine osmolality, indicating kidneys’ concentrating ability. Normal 1.016–1.022. Isosthenuria (1.010) means urine osmolality same as plasma.
  • Urinary Electrolytes: (Sodium, potassium, chloride). “Normal” values depend on intake and regulation by kidneys. Fractional excretion of sodium (%FENa) assists with diagnostic dilemmas.

Electrolytes, Other Minerals, and Trace Elements

• Sodium (Na):
  • Hyponatremia (<136 mEq/L): May be hyper-, euvo-, or hypovolemic. Hypovolemic from GI/renal losses; euvolemic (dilutional) from impaired free water excretion (e.g., SIADH, glucocorticoid deficiency, hypothyroidism); hypervolemic from CHF, cirrhosis, nephrotic syndrome. Can cause seizures.
  • Hypernatremia (>145 mEq/L): Common in impaired thirst, inability to replete water deficit (insensible, renal, GI losses). Increases serum osmolality.
• Potassium (K):
  • Hypokalemia (<3.5 mEq/L): Can cause EKG abnormalities.
  • Hyperkalemia (>5 mEq/L):.
  • Factitious Elevation: May occur if erythrocytes in blood samples undergo haemolysis prior to analysis.
• Chloride (Cl): Renal excretion increases during metabolic alkalosis, leading to reduced serum chloride. Metabolic or respiratory acidosis can elevate serum chloride. Bromide toxicity can cause falsely elevated chloride levels.
• Calcium (Ca): Total serum calcium (commonly reported) is less clinically significant than ionized calcium, which is the physiologically active moiety. Alkalosis increases protein binding of calcium, reducing free fraction; acidosis has opposite effect. Hypocalcemia can cause seizures in neonates.
• Phosphate (P): Major intracellular anion, important for metabolism of proteins, lipids, carbohydrates.
• Magnesium (Mg): Affects CNS (personality changes, convulsions, psychosis) and heart (prolonged QT interval, arrhythmias).
• Chromium (Cr): Cofactor for insulin and glucose/cholesterol/triglyceride metabolism. Deficiency may lead to hypercholesterolemia, risk factor for ASCVD.
• Zinc (Zn): Essential for growth, immune function, wound healing. Hypozincemia linked to various conditions.
• Copper (Cu): (Not detailed beyond mention of being a trace element).
• Manganese (Mn): (Not detailed beyond mention of being a trace element).

Arterial Blood Gases (ABGs) and Acid-Base Balance

• Assessment: Assesses acid-base status using pH, PaCO2, and HCO3-.
• Parameters:
  • pH: Normal range 7.35–7.45. Below 7.35 is acidemia, above 7.45 is alkalemia. Inversely related to hydrogen concentration.
  • PaCO2 (Partial Pressure of Carbon Dioxide): Most abundant acid, controlled by respiratory regulation.
  • HCO3- (Bicarbonate): Most abundant base, concentrations maintained by the kidney.
• Four Primary Disorders: Categorized by type (acidosis vs. alkalosis) and origin (metabolic vs. respiratory).
• Anion Gap: Used to determine primary cause of metabolic acidosis.
• Medications: Frequently implicated in acid-base disorders.

Pulmonary Function Tests (PFTs)

• Purpose: Provide objective and quantifiable measures of lung function; useful in diagnosis, evaluation, and monitoring of respiratory disease.
• Spirometry: Most frequently used PFT, measures movement of air into and out of lungs during breathing maneuvers. Aids in diagnosis of asthma, COPD.
  • Forced Expiratory Volume in One Second (FEV1): Most clinical relevance as an indicator of airway function. ≥80% predicted is normal.
  • Forced Vital Capacity (FVC): Total amount of air exhaled after maximal inhalation.
  • Flow-Volume Curves: Illustrate patterns for normal, obstructive, restrictive, and mixed diseases. Concavity in expiratory portion for obstruction; smaller FVC for restriction.
• Lung Volumes Assessment: (As determined by body plethysmography) measures the amount of gas contained in the lungs. Necessary to define restriction, as spirometry alone does not diagnose it.
• Carbon Monoxide Diffusion Capacity (DLCO): Measures gas exchange.
• Bronchial Provocation Tests (BPTs): Measure reactivity of airways to agents that induce narrowing (e.g., methacholine, histamine). Aid in asthma diagnosis, evaluate drug effects on airway hyperreactivity, and potential drug effectiveness.

Liver and Gastroenterology Tests

• Liver Functions: Synthesis of proteins (albumin, clotting factors), processing/breakdown of amino acids (ammonia/urea), carbohydrate/lipid metabolism, detoxification/excretion of endogenous/exogenous substances (drugs/toxins), bilirubin metabolism.
• Liver Function Test (LFT) Panel: Varies slightly between hospitals but generally includes aminotransferases (AST, ALT), bilirubin, alkaline phosphatase (ALP), and albumin. LFT is a misnomer as not all tests measure function; aminotransferases reflect liver injury.
• Interpretation Context: LFTs must always be interpreted with a clear understanding of the clinical context and other laboratory abnormalities. A single set of LFTs can have widely differing significance in different clinical settings.
• Tests of Synthetic Liver Function:
  • Albumin: Synthesized in liver. Levels reflect synthetic capacity. Inadequate function limited mainly to hepatic cirrhosis or massive liver damage. Has a half-life of 20 days. Low levels can indicate malnutrition, liver disease, or hydration status.
  • Prealbumin (Transthyretin): Short half-life (2 days), smaller body pool, more sensitive to protein nutrition, less affected by liver disease/hydration than albumin. Routinely used to monitor patients on TPN or tube feeding.
  • Prothrombin Time (PT) and International Normalized Ratio (INR): Reflect synthesis of clotting factors. Prolonged in severe liver damage.
• Tests of Excretory Liver Function and Cholestasis:
  • Bilirubin: Total, direct, indirect. Elevated in cholestasis, haemolysis, genetic syndromes (Gilbert, Crigler-Najjar, Dubin-Johnson, Rotor).
  • Alkaline Phosphatase (ALP): Elevated in cholestasis; also in bone disease, pregnancy, developing bone.
  • Gamma-Glutamyl Transferase (GGT): Elevated in cholestasis.
• Tests of Hepatocellular Injury:
  • Aminotransferases (AST, ALT): Enzymes primarily inside hepatocytes, released into serum in greater quantities with hepatocyte injury. (AST formerly SGOT, ALT formerly SGPT).
• Tests of Detoxifying Liver Function:
  • Ammonia (NH3+): Product of bacterial protein metabolism in the gut. Elevated levels associated with hepatic encephalopathy, Reye syndrome, urea cycle disorders, valproic acid use, impaired renal function.
• Specific Diseases:
  • Viral Hepatitis (HAV, HBV, HCV, HDV, HEV): Diagnosed by serology (antigen/antibody detection), nucleic acid amplification techniques (NAATs), and sometimes cell culture. HBsAg indicates active infection; HBeAg indicates high viral load and infectivity.
  • Hemochromatosis: Disorder of iron metabolism, involves liver.
  • Pancreatitis: Diagnosed using amylase and lipase. Serum amylase has low specificity; lipase is preferred as it is confounded by fewer factors.
  • Helicobacter pylori (H. pylori) Infection: Related to peptic ulcer disease.
  • Clostridium difficile (C. difficile) Colitis: Major cause of hospital-acquired colitis.

Hematology: Red and White Blood Cell Tests

• Complete Blood Count (CBC): Frequently ordered, provides information on cellular and noncellular elements of blood. Includes hemoglobin, RBC indices, WBC count, WBC differential, platelet count, reticulocyte count, ESR.
• Red Blood Cells (RBCs):
  • Hemoglobin (Hgb): Normal ranges males 14–17.5 g/dL, females 12.3–15.3 g/dL.
  • Anemia: Reduction in RBCs or Hgb. Classified by RBC indices (MCV, MCH, MCHC) into microcytic, normochromic/normocytic, or macrocytic.
    • Microcytic Anemia (MCV ≤80 fL): Possible causes include iron deficiency (low serum iron, high TIBC, low ferritin).
    • Normochromic, Normocytic Anemia (MCV 81–99 fL): Possible causes include acute blood loss, hemolytic anemia, anemia of chronic disease.
    • Macrocytic Anemia (MCV >100 fL): Possible causes include vitamin B12 deficiency (high serum methylmalonate, high serum homocysteine), folic acid deficiency (low serum folate, high serum homocysteine), drug-induced bone marrow toxicity.
  • Erythrocyte Sedimentation Rate (ESR): Inflammatory marker, used as sensitive marker of treatment response. Also useful in rheumatologic diseases.
• White Blood Cells (WBCs):
  • WBC Count: Normal range 4.4–11.3 × 103 cells/mL. Neutropenia in neonates is a highly significant finding indicating serious infection.
  • WBC Differential: Percentages of five mature WBC types. A change in differential (e.g., increased neutrophils) can indicate infection even with a normal total WBC count. Lymphocytes are most prevalent in children up to 5-6 years, then neutrophils predominate.
  • CD4 T Lymphocyte Count: Used in HIV-positive patients as a marker of progression to AIDS and risk of opportunistic infections.
• Drug-Induced Alterations:
  • RBCs: Reduced by NSAID-induced GI bleeding or hemolytic anemia in G6PD deficiency with oxidizing drugs.
  • WBCs: Commonly decreased following cytotoxic chemotherapy, especially neutrophils due to faster turnover.
  • Glucocorticosteroids: Lymphotoxic (decreases lymphocyte count) but increase apparent neutrophil count (demargination).
  • Antifolates (e.g., methotrexate): Can cause macrocytic, hypochromic anemia.

Hematology: Blood Coagulation Tests

• Hemostasis Evaluation: Organized by tests for platelets, coagulation, and clot degradation.
• Platelet Tests:
  • Platelet Count: Normal range 150,000–450,000/µL. Lower in newborns. Automated methods are common, but interferences (RBC fragments, platelet clumping, satellitism) can occur. Critical value >800,000 or <20,000 µL.
  • Mean Platelet Volume (MPV):.
  • Platelet Aggregation: Measured by aggregometer; light transmittance aggregometry (LTA) is gold standard but expensive and has reproducibility issues.
  • Bleeding Time (BT): Measures time for small cut to stop bleeding. Many drawbacks, replaced by platelet function tests.
• Coagulation Tests: Used to identify deficiencies of coagulation factors, thrombotic disorders, and monitor anticoagulant therapy. Lack of standardization across methods can lead to variation in results and interpretation.
  • Prothrombin Time (PT) / International Normalized Ratio (INR):
    • PT: Assesses integrity of extrinsic and common pathways (factors II, V, VII, X). Normal range 10-13 seconds.
    • INR: Calibration method to standardize PT results, considering reagent sensitivity (ISI). Normal range 0.8–1.1; therapeutic range 2–3 (most indications) or 2.5–3.5 (depending on indication for warfarin).
  • Activated Partial Thromboplastin Time (aPTT): Assesses intrinsic and common pathways (factors VIII, IX, XI, XII, V, X, II). Normal range 25-35 seconds. Used to monitor heparin therapy.
  • Activated Clotting Time (ACT):.
  • Thrombin Time (TT):.
  • Fibrinogen Assay:.
• Disseminated Intravascular Coagulation (DIC): Laboratory findings are highly variable, complex, and difficult to interpret. Typically, prolonged PT/aPTT, decreased platelet count, elevated FDPs, and increased D-dimer are seen.
• Antithrombotic and Anticoagulant Medications:
  • Platelet Inhibitors (Aspirin, Clopidogrel): Inhibit platelet aggregation.
  • Oral Anticoagulants (Warfarin): Inhibits vitamin K-dependent clotting factors (II, VII, IX, X) and proteins C and S. Monitored by INR.
  • Direct Oral Anticoagulants (DOACs): Dabigatran (thrombin inhibitor), Rivaroxaban/Apixaban (factor Xa inhibitors). aPTT provides qualitative but not quantitative information for dabigatran; even less sensitive for factor Xa inhibitors.
• Point-of-Care Coagulation Testing: Devices available for PT/INR, ACT, D-dimer, and platelet function tests. Easy to use, adaptable to various environments, minimal sample processing, but generally less precise than central lab systems.

Infectious Diseases: Laboratory Diagnosis

• Microbiological Diagnosis: Requires identification of the pathogen. Clinical diagnosis (signs/symptoms) combined with lab data often assesses severity and influences management.
• Common Laboratory Tests for Bacteria:
  • Direct Microscopic Examination: Using specialized stains (e.g., Gram stain for cell morphology) and bacterial culture.
  • Bacterial Culture Techniques: “Gold standard” for identification and susceptibility testing.
  • Antimicrobial Susceptibility Testing: Determines activity of antibiotics against a specific pathogen. Methods include broth macrodilution (gold standard, determines MIC), broth microdilution, and agar dilution.
    • Minimum Inhibitory Concentration (MIC): Lowest antibiotic concentration that completely inhibits visible growth.
    • Antibiogram: Cumulative antibiotic susceptibility test data, based on input from multidisciplinary committees.
• Fungal Identification: Traditionally based on morphological characteristics and culture (“gold standard”). DNA sequence analysis and molecular characteristics are gaining role. Direct microscopic examination with specific stains (e.g., Alcian blue, Brown and Brenn, Calcofluor white) and serology (antibody testing).
• Viral Identification: Laboratory techniques include cell culture (historically gold standard, now declining in routine use but important for new virus discovery, drug resistance), cytology/histology, electron microscopy (EM), antigen detection, Nucleic Acid Amplification Techniques (NAATs), and serologic testing.
  • Antigen Detection: Uses immunoassays (IFA, ELISA, ICA); rapid detection (within minutes) of specific antigens (e.g., rapid influenza diagnostic tests).
  • NAATs: Detects specific DNA/RNA sequences (e.g., PCR). Becoming cornerstones for virus detection.
  • Serologic Testing: Detects antibodies; rise in titre indicates ongoing infection, fall indicates convalescence. Often not useful in immunocompromised patients for fungal infections.
• Specific Infections:
  • Meningitis: Infectious diseases medical emergency. Lumbar puncture to obtain CSF for analysis (appearance, glucose, protein, WBC count/differential, Gram stain, cultures, antigen detection). Head CT may precede LP to rule out space-occupying lesions.
  • Pneumonia: Diagnosis supported by sputum culture. Urinary antigen tests or NAATs for atypical bacteria (e.g., Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae).
  • HIV-1 Infection: Lab tests for diagnosis, monitoring progression/antiretroviral therapy response, and blood donor screening. Involves HIV-1/2 antibody tests, p24 antigen, and HIV-1 NAT. CD4 T lymphocyte counts and HIV-1 RNA levels (viral loads) are markers for progression to AIDS and treatment success.
  • Tuberculosis (TB): Mycobacterium tuberculosis is difficult to culture. Tuberculin skin test (TST), nucleic acid amplification tests (NAATs), and interferon-gamma release assays (IGRAs) are used . Susceptibility testing for Non-Tuberculous Mycobacteria (NTM) is recommended for clinically significant isolates.
  • Acute Phase Reactants: ESR and C-reactive protein (CRP) are inflammatory markers that may be elevated and support the diagnosis of infection.
• Antimicrobial Toxicity Monitoring: Antimicrobial agents have a range of toxicity reflected in laboratory test abnormalities (e.g., flucloxacillin-induced neutropenia). Monitoring plans should incorporate both disease progress and drug toxicity/efficacy. Some antimicrobials (e.g., cefoxitin) can interfere with creatinine assays, causing falsely elevated levels. For drugs with a narrow therapeutic index (aminoglycosides, vancomycin, chloramphenicol), TDM is important.

Rheumatologic Diseases

• Diagnosis and Management: Rely primarily on patient medical history, symptoms, and physical examination. Laboratory tests assist in diagnosis but are often non-specific.
• Nonrheumatologic Tests (General):
  • CBC: Anemia (normochromic-normocytic or microcytic) is common in chronic inflammatory diseases (RA, SLE). Microcytic anemia can be due to iron deficiency (e.g., GI blood loss from NSAIDs).
  • Serum Chemistry Panel: Abnormalities (e.g., elevated BUN, creatinine) may indicate renal involvement (e.g., lupus nephritis).
  • Urinalysis: Useful for detecting proteinuria, hematuria, pyuria (seen in SLE and with certain drug therapies).
• Specific Rheumatologic Tests:
  • Erythrocyte Sedimentation Rate (ESR) and C-reactive Protein (CRP): Inflammatory markers, used to assess disease activity and response to treatment.
  • Antinuclear Antibodies (ANA): Non-specific, but positive tests common in Systemic Lupus Erythematosus (SLE).
  • Rheumatoid Factor (RF): Positive in rheumatoid arthritis (RA).
  • Anticitrullinated Protein Antibodies: Highly specific for RA.
• Drug-Induced Alterations: Microcytic anemia from GI blood loss due to NSAIDs.

Tumor Markers and Cancer Diagnosis

• Definition: Substances found in blood, other body fluids, or tumor tissues, used to identify presence of some cancers, of occult cancers (screening, early detection), determining extent of disease (staging), estimating prognosis, predicting/assessing treatment response, monitoring for disease recurrence/progression.
• Common Tumor Markers (in Blood): Alpha-fetoprotein (AFP) (hepatocellular cancer), carcinoembryonic antigen (CEA), prostate-specific antigen (PSA).
• Molecular Tests: Genetic analysis is crucial for personalized cancer therapies (e.g., EGFR mutations in non-small cell lung cancer, HER2 amplification in breast cancer, EML4-ALK320, 326].
• Different Reference Ranges: These alterations result in different normal reference ranges compared to adults, and values may also differ between pediatric age groups. Clinicians must use age-appropriate reference ranges.
• Total Blood Volume: Children have a much smaller total blood volume than adults. Standard blood samples represent a higher percentage of total blood volume, requiring smaller sample sizes. Frequent blood draws should be avoided in critically ill neonates.
• Clinical Presentation:
  • Symptoms: Similar to adults, but manifestations can differ. CNS irritability due to electrolyte imbalances (e.g., hypernatremia) may manifest as a high-pitched cry in infants.
  • Seizures: Hypocalcemia is more likely to manifest as seizures in neonates and young infants due to CNS immaturity. Neonates may have nonspecific symptoms for many disorders (e.g., poor feedings, lethargy, vomiting for sepsis, meningitis, hypocalcemia).
  • Communication: Young pediatric patients cannot communicate symptoms.
• Specific Pediatric Considerations:
  • Serum Albumin: Lower in newborns, increasing with age .
  • Alkaline Phosphatase (ALP): Can be twofold to threefold higher than adults due to developing bone.
  • Serum Creatinine (SCr): Varies with age, reflecting skeletal muscle mass and kidney function maturation .
  • Electrolytes and Minerals: Age-related differences due to body compartment changes, immature neonatal kidney function, and increased requirements for growth.
  • Neutropenia in Neonates: A highly significant finding and often the first abnormal lab result indicating neonatal bacterial infection.
  • WBC Differential: Lymphocytes are most prevalent in children up to 5-6 years of age, after which neutrophils predominate.
  • Platelet Count: May be lower in newborns compared to adults; adult values reached after one week.
• Pharmacokinetic Changes: Physiological events (changes in body water, body fat, plasma proteins, hormonal composition) influence drug disposition and dose requirements from neonates to adolescents. Children are not ‘miniature adults’; adult doses scaled by body weight may not be safe or effective.

Men’s Health

• Prostate-Specific Antigen (PSA): Used for screening, staging, and monitoring treatment of prostate cancer.
• DNA Methylation Assay: Assesses DNA methylation in prostate tissue; abnormality in specific genes is a positive test for prostate cancer.
• Testosterone:
  • Total Testosterone: Reflects total concentration (free and protein-bound).
  • Free Testosterone: Reflects only the unbound (physiologically active) portion. Indicated when SHBG (sex hormone-binding globulin) concentrations are altered.
  • SHBG: Increased by cirrhosis, hyperthyroidism, old age, estrogens, anticonvulsants. Decreased by hypothyroidism, obesity, excessive testosterone supplements.
• Hypogonadism: Symptomatic hypogonadism generally associated with total testosterone <200–230 ng/dL.