Questions
3–5 questions per university paper
Difficulty
Medium-Hard
Importance
High yield for MBBS and BMLT/B.Pharm clinical chemistry sections
Overview
Organ function tests are diagnostic biochemical panels used to evaluate the physiological health and metabolic activity of critical body organs. For university and board exams, mastering these is essential to correlate clinical chemistry markers with pathological states, representing a high-yield area for both theoretical papers and viva voce.
Liver Function Tests (LFTs)
LFTs evaluate hepatic health by measuring enzymes, proteins, and bilirubin levels in the blood. Examiners focus on differentiating between hepatocellular damage and cholestatic patterns.
- Bilirubin: Elevated in jaundice (pre-hepatic, hepatic, post-hepatic)
- ALT and AST: Markers of hepatocellular injury
- ALP (Alkaline Phosphatase): Marker of biliary obstruction/cholestasis
- Serum Albumin: Indicates chronic synthetic liver function
- Prothrombin Time (PT): Measures clotting factor synthesis by the liver
Kidney Function Tests (KFTs/RFTs)
These tests assess the glomerular filtration rate and the excretory capability of the kidneys. Understanding the balance between nitrogenous waste production and renal clearance is fundamental.
- Blood Urea Nitrogen (BUN): Sensitive but less specific for GFR
- Serum Creatinine: Primary clinical marker for GFR estimation
- Creatinine Clearance: Formula = (Urine Cr * Urine Vol) / Serum Cr
- GFR (Glomerular Filtration Rate): Gold standard indicator of renal function
- Uric Acid: Assessed for gout and renal impairment linkage
Thyroid Function Tests (TFTs)
TFTs diagnose thyroid disorders by measuring the feedback loop between the pituitary gland and the thyroid gland. The relationship between TSH and T3/T4 levels is a classic exam favorite.
- TSH (Thyroid Stimulating Hormone): The most sensitive indicator of thyroid status
- Free T4 (Thyroxine): Direct measure of circulating active hormone
- Primary Hypothyroidism: High TSH, Low T4
- Primary Hyperthyroidism: Low TSH, High T4
- TPO Antibodies: Diagnostic for autoimmune thyroiditis (Hashimoto's)
Adrenal Function Tests
These assess the secretory activity of the adrenal cortex, specifically focusing on cortisol regulation. Exams often test the understanding of the HPA axis negative feedback mechanism.
- Serum Cortisol: Circadian variation requires morning testing
- Dexamethasone Suppression Test: Used to diagnose Cushing's Syndrome
- ACTH Stimulation Test: Used to assess adrenal insufficiency (Addison's disease)
- Aldosterone/Renin Ratio: Primary screening for hyperaldosteronism
Formula Sheet
Creatinine Clearance (ml/min) = (Urine Cr * Urine Volume) / (Serum Cr * Time)
Fractional Excretion of Sodium (FENa) = (UNa * PCr) / (PNa * UCr) * 100
Exam Tip
Always interpret LFTs and KFTs as a panel; never diagnose based on a single marker in isolation, as clinicians look for patterns of elevation.
Common Mistakes
- Confusing AST/ALT specificity, forgetting that AST is also present in cardiac and muscle tissue.
- Assuming high serum creatinine always equals acute renal failure without considering muscle mass or hydration.
- Neglecting the role of negative feedback loops when interpreting TSH vs. T4 levels in exam case studies.
More Revision Notes
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