Clinical Chemistry

Clinical Chemistry

Clinical chemistry is the branch of laboratory medicine concerned with analysis of body fluids (blood, urine, CSF) to provide diagnostic, monitoring, and prognostic information. It encompasses biochemical marker testing, quality control, and reference interval establishment.

Specimen Types & Handling

  • Whole Blood: Collected in EDTA (prevents clotting by chelating Ca²+) for hematology; Li-heparin for chemistry
  • Serum: Blood clotted → centrifuge → liquid part. No fibrinogen, no clotting factors. Used for most biochemistry tests.
  • Plasma: Blood with anticoagulant → centrifuge → liquid. Contains fibrinogen. For coagulation tests (PT, PTT).
  • Urine: Spot (random) or 24-hour collection. Creatinine clearance, protein quantification, hormones, toxicology.
  • CSF: Lumbar puncture; glucose, protein, cells, cultures, oligoclonal bands.
  • Hemolysis, Lipemia, Icterus (HLI): Major interferents in clinical chemistry measurements — must be recognized and managed.

Key Clinical Chemistry Tests

  • Blood Glucose: Fasting 70–100 mg/dL; Post-load <140 mg/dL. Glucose oxidase or hexokinase methods. HbA1c for monitoring.
  • Creatinine & BUN: Markers of kidney function. Creatinine generated from creatine phosphate at constant rate. BUN (Blood Urea Nitrogen) reflects urea. BUN:Cr ratio: >20:1 = pre-renal azotemia; <15:1 = intrinsic renal disease; post-renal variable. eGFR calculated from creatinine, age, sex (CKD-EPI or MDRD formula).
  • Electrolytes: Na+, K+, Cl⁻, HCO₃⁻ — measured by ion-selective electrodes (ISE)
  • Liver Function Tests: ALT (hepatocellular damage), AST (less specific), ALP (cholestasis/bone), GGT (sensitive alcohol marker), Total/Direct/Indirect Bilirubin (hyperbilirubinemia type), Albumin (synthetic function), PT (coagulation, also synthetic function)
  • Lipid Panel: Total Cholesterol, LDL, HDL, Triglycerides. Friedewald equation: LDL = TC − HDL − TG/5 (valid only if TG <400 mg/dL).
  • Thyroid Function: TSH (best screening test), Free T4, Free T3.
  • Cardiac Markers: Troponin I/T (MI — most sensitive/specific; rises within 3h, peaks 12–24h, normalizes 7–14 days), CK-MB (earlier marker), BNP/NT-proBNP (heart failure), Myoglobin (earliest but not specific)

Point-of-Care Testing (POCT)

Rapid tests performed at or near the patient. Examples: Glucose meters, urine dipstick, ABG, coagulometers, bedside troponin, pregnancy test (β-hCG), COVID antigen test. Advantages: Rapid results, ease of use. Disadvantages: Less precision, quality control challenges, higher per-test cost.

Quality Control (QC) in Clinical Labs

  • Accuracy: Closeness to true value (reduced by calibration with standards)
  • Precision: Reproducibility of results (reduced by within-run and between-run variability)
  • Levey-Jennings Chart: QC values plotted over time; Westgard rules identify systematic errors (shift, trend) and random errors
  • Reference Intervals: Values from 95% of healthy reference population (mean ±2 SD for normal distribution)
  • Critical Values (Panic Values): Life-threatening results requiring immediate clinician notification (e.g., K+ <2.5 or >6.5 mEq/L, glucose <40 or >500 mg/dL)

Urinalysis

Physical (color, clarity, SG, pH), Chemical (dipstick: glucose, protein, blood, ketones, bilirubin, nitrite, leukocyte esterase), Microscopic (RBCs, WBCs, casts, crystals). Proteinuria >150 mg/day = pathological. Microalbuminuria (30–300 mg/day) = early diabetic nephropathy marker.

Quiz - Exam Preparation Strategy

When studying Quiz for your final board exams, it is critical to focus on the core concepts and fundamental formulas. Relying strictly on NCERT textbook solutions and practicing previous year questions (PYQs) is the proven methodology for scoring high marks. Avoid rote memorization and instead focus on the logical application of the theories presented in this chapter.

⚠️ Common Mistakes to Avoid

❓ Frequently Asked Questions

How can I quickly memorize the concepts of Quiz?

The most effective way is to create short, handwritten revision notes and continuously test your knowledge using our interactive Mock Tests. Spaced repetition and active recall are much better than passive reading.

What type of questions are most commonly asked from Quiz?

Board exams tend to favor conceptual application questions and direct formula-based derivations from the NCERT syllabus. Ensure you have solved every single exercise in the official textbook.

Is reading the NCERT book enough for this chapter?

Yes, the NCERT textbook is the absolute gold standard for board exams. However, to improve your speed and accuracy during the actual exam, you must supplement your reading by solving timed mock tests and objective questions.