14 clinical MCQs in Chemical Pathology. A 55-year-old diabetic patient presents to the emergency department with confusion, rapid
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Q1. A 55-year-old diabetic patient presents to the emergency department with confusion, rapid breathing, and fruity breath odor. Random blood glucose is 28 mmol/L. (
- Define diabetic ketoacidosis (DKA). (2 marks)
- List FIVE biochemical investigations you would request to confirm and manage DK
- (5 marks)
- Explain the biochemical basis for the acid-base disturbance in DK
- (3 marks) #### ANSWER TO QUESTION 1
Answer: Define diabetic ketoacidosis (DKA). (2 marks)
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Q2. A 45-year-old man presents with severe chest pain radiating to the left arm. ECG shows ST-segment elevation. (
- Name FOUR cardiac biomarkers used in the diagnosis of acute myocardial infarction. (4 marks)
- Describe the time course of troponin elevation and its clinical significanc
- (4 marks)
- State TWO conditions other than myocardial infarction that can cause troponin elevation. (2 marks) #### ANSWER TO QUESTION 2
- Four cardiac biomarkers (4 marks - 1 mark each) - Cardiac Troponin I (cTnI) - Cardiac Troponin T (cTnT) - Creatine Kinase-MB (CK-M
Answer: Name FOUR cardiac biomarkers used in the diagnosis of acute myocardial infarction. (4 marks)
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Q3. A 35-year-old woman complains of fatigue, weight gain of 10 kg over 6 months, cold intolerance, and constipation. (
- List FOUR thyroid function tests you would request. (4 marks)
- Describe the expected laboratory findings in primary hypothyroidism. (3 marks)
- Differentiate between primary and secondary hypothyroidism based on laboratory results. (3 marks) #### ANSWER TO QUESTION 3
- Four thyroid function tests (4 marks - 1 mark each) - Thyroid Stimulating Hormone (TSH) - Free Thyroxine (Free T4) - Free Triiodothyronine (Free T3) - Thyroid peroxidase antibodies (TPO antibodies)
Answer: List FOUR thyroid function tests you would request. (4 marks)
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Q4. Explain the role of the kidney in maintaining acid-base balance. (
- Describe THREE mechanisms by which the kidney regulates acid-base balanc
- (6 marks)
- Define metabolic acidosis and calculate the anion gap given the following values: Na+ 140 mmol/L, Cl- 100 mmol/L, HCO3- 15 mmol/L. (4 marks) #### ANSWER TO QUESTION 4
- Three mechanisms of renal acid-base regulation (6 marks - 2 marks each) - Bicarbonate Reabsorption: The proximal tubule reabsorbs approximately 80-90% of filtered bicarbonate - H+ is secreted into tubular fluid, combines with HCO3- to form H2CO3, which dissociates to CO2 and H2O - CO2 diffuses back into tubular cells and is reformed into HCO3- which enters blood - Excretion of Titratable Acids (Phosphate Buffer System): H+ ions are secreted and buffered by HPO4²- forming H2PO4- - This allows excretion of H+ without excessive lowering of urine pH - Accounts for about 30-40% of acid excretion - Ammonia Buffer System: Glutamine is metabolized in renal tubular cells to produce ammonia (NH3) and bicarbonate - NH3 diffuses into tubular lumen and combines with H+ to form NH4+ (ammonium) - NH4+ is trapped in tubular fluid and excreted in urine - Most important mechanism in chronic acidosis
- Definition and anion gap calculation (4 marks) Definition (2 marks): Metabolic acidosis is a primary decrease in plasma bicarbonate (HCO3- <22 mmol/L) with or without compensatory decrease in pCO2, resulting in decreased blood pH (<7.35) Anion Gap Calculation (2 marks): - Formula: Anion Gap = (Na+) - (Cl- + HCO3-) - Calculation: 140 - (100 + 15) = 25 mmol/L - Normal anion gap = 8-12 mmol/L - This represents HIGH anion gap metabolic acidosis --
Answer: Describe THREE mechanisms by which the kidney regulates acid-base balanc
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Q5. A 60-year-old man with chronic back pain is found to have hypercalcemia (serum calcium 3.2 mmol/L). (
- List FOUR biochemical investigations you would perform to evaluate hypercalcemi
- (4 marks)
- Describe the biochemical findings that would suggest primary hyperparathyroidism. (3 marks)
- State THREE clinical complications of prolonged hypercalcemi
- (3 marks) #### ANSWER TO QUESTION 5
Answer: List FOUR biochemical investigations you would perform to evaluate hypercalcemi
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Q6. A 28-year-old woman presents with jaundice. Laboratory results show: Total bilirubin 85 μmol/L (unconjugated 70 μmol/L), ALT 350 U/L, AST 320 U/L, ALP 150 U/L. (
- Classify jaundice based on pathophysiology and give ONE example of each typ
- (6 marks)
- Based on the laboratory results above, what type of jaundice does this patient likely have? Justify your answer. (4 marks) #### ANSWER TO QUESTION 6
- Classification of jaundice (6 marks - 2 marks per typ
- - Pre-hepatic (Hemolyti
Answer: Classify jaundice based on pathophysiology and give ONE example of each typ
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Q7. Discuss the clinical utility and interpretation of lipid profile tests. (
- List FIVE components typically measured in a standard lipid profil
- (5 marks)
- Explain the classification of lipoproteins based on density and their atherogenic potential. (5 marks) #### ANSWER TO QUESTION 7
- Five components of lipid profile (5 marks - 1 mark each) - Total cholesterol - Triglycerides - High-Density Lipoprotein Cholesterol (HDL
- - Low-Density Lipoprotein Cholesterol (LDL
Answer: List FIVE components typically measured in a standard lipid profil
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Q8. A 50-year-old chronic alcoholic presents with abdominal pain and vomiting. Serum amylase is 1200 U/L. (
- What is the most likely diagnosis? List THREE other biochemical tests useful in confirming this diagnosis. (4 marks)
- Explain the biochemical basis for elevated serum amylase in this condition. (3 marks)
- State THREE causes of elevated serum amylase other than your diagnosis in (a). (3 marks) #### ANSWER TO QUESTION 8
- Three other causes of elevated serum amylase (3 marks - 1 mark each) - Parotitis (mumps, salivary gland diseas
- - Perforated peptic ulcer or intestinal obstruction - Renal failure (decreased clearanc
Answer: What is the most likely diagnosis? List THREE other biochemical tests useful in confirming this diagnosis. (4 marks)
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Q9. A 40-year-old woman presents with polyuria, polydipsia, and bone pain. Serum calcium is elevated at 3.0 mmol/L. (
- Explain the relationship between calcium and parathyroid hormone (PTH). (4 marks)
- List THREE biochemical tests used to evaluate metabolic bone disorders. (3 marks)
- Differentiate between primary and secondary hyperparathyroidism based on biochemical findings. (3 marks) #### ANSWER TO QUESTION 9
- Differentiation between primary and secondary hyperparathyroidism (3 marks) Primary Hyperparathyroidism: - High PTH with HIGH serum calcium (hypercalcemi
Answer: Explain the relationship between calcium and parathyroid hormone (PTH). (4 marks)
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Q10. Describe the principles of quality control in clinical biochemistry laboratories. (
- Differentiate between accuracy and precision in laboratory testing. (4 marks)
- Explain the components of internal quality control (IQC). (4 marks)
- State TWO purposes of external quality assessment (EQA). (2 marks) #### ANSWER TO QUESTION 10
- Accuracy vs Precision (4 marks) Accuracy (2 marks): - The closeness of a measured value to the true or accepted reference value - Measures systematic error or bias - Example: If true glucose is 5.0 mmol/L and test gives 5.1 mmol/L repeatedly, it's accurate Precision (2 marks): - The reproducibility or repeatability of measurements - Measures random error - Example: If repeated measurements give 5.0, 5.1, 4.9, 5.0 mmol/L, this shows good precision - Can have precise results that are not accurate (consistent but wrong)
- Components of Internal Quality Control (4 marks) - QC Materials (1 mark): Use of control samples with known values run alongside patient samples - Include normal and abnormal level controls - Levey-Jennings Charts (1 mark): Plot QC results over time to monitor analytical performance - Establish mean and standard deviation limits - Westgard Rules (1 mark): Statistical rules to detect analytical errors - Examples: 1-2s (warning), 1-3s (rejection), 2-2s, R-4s rules - Pre-analytical, Analytical, Post-analytical phases (1 mark): Monitor all phases of testing process - Include specimen collection, handling, analysis, and result reporting
- Two purposes of External Quality Assessment (2 marks - 1 mark each) - Compare laboratory performance with other laboratories (inter-laboratory comparison) - Identify systematic errors and ensure method standardization across laboratories --- ## SECTION B: LONG ESSAY QUESTIONS (20 Marks Each) ### Answer ANY ONE Question --
Answer: Differentiate between accuracy and precision in laboratory testing. (4 marks)
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Q11. Write comprehensive notes on Diabetes Mellitus covering: (
- Classification of diabetes mellitus. (4 marks)
- Biochemical criteria for diagnosis of diabetes mellitus. (6 marks)
- Role of HbA1c in diagnosis and monitoring of diabetes. (5 marks)
- Complications of diabetes mellitus and relevant biochemical monitoring. (5 marks) #### ANSWER TO QUESTION 11
- Role of HbA1c (5 marks) What is HbA1c (1 mark): - Glycated hemoglobin - glucose attached non-enzymatically to hemoglobin - Reflects average blood glucose over preceding 2-3 months (lifespan of RB
Answer: Classification of diabetes mellitus. (4 marks)
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Q12. Discuss Renal Function Tests in detail: (
- Describe the biochemical assessment of glomerular function. (8 marks)
- Explain the biochemical assessment of tubular function. (6 marks)
- Discuss the role of urinalysis in evaluating renal diseas
- (6 marks) #### ANSWER TO QUESTION 12
- - Stage 2: 60-89 - Stage 3: 30-59 - Stage 4: 15-29 - Stage 5: <15 (kidney failur
Answer: Describe the biochemical assessment of glomerular function. (8 marks)
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Q13. Write detailed notes on Liver Function Tests: (
- Describe the biochemical tests used to assess hepatocellular function. (8 marks)
- Explain the biochemical tests used to assess cholestasis and biliary obstruction. (6 marks)
- Discuss the pattern of liver function test abnormalities in different types of liver diseas
- (6 marks) #### ANSWER TO QUESTION 13
- Bilirubin:* - Normal: <5 μmol/L - Elevated in hepatobiliary disease *Indirect (Unconjugate
Answer: Describe the biochemical tests used to assess hepatocellular function. (8 marks)
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Q14. A 25-year-old woman presents with heat intolerance, palpitations, weight loss, and tremors. Physical examination reveals exophthalmos and thyroid enlargement. (
- List FOUR thyroid function tests you would request. (4 marks)
- Describe the expected laboratory findings in hyperthyroidism (thyrotoxicosis). (3 marks)
- Differentiate between Graves' disease and toxic multinodular goiter based on clinical and laboratory features. (3 marks) #### ANSWER TO QUESTION 14
- Four thyroid function tests (4 marks - 1 mark each) - Thyroid Stimulating Hormone (TSH) - Free Thyroxine (Free T4) - Free Triiodothyronine (Free T3) - TSH receptor antibodies (TRA
- or Thyroid stimulating immunoglobulins (TSI) (Accept: Thyroid peroxidase antibodies, radioactive iodine uptake scan)
Answer: List FOUR thyroid function tests you would request. (4 marks)