Practice 7 structured short- and long-answer medical questions on Chemical Pathology Practice Examination. Review model answers for exam revision.
Answer: 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 ( - Definition of Diabetic Ketoacidosis (2 marks) - DKA is a life-threatening acute metabolic complication of diabetes mellitus characterized by hyperglycemia (blood glucose >11 mmol/L), ketonemia/ketonuria, and metabolic acidosis (pH <7.3, bicarbonate <15 mmol/L) - It results from absolute or relative insulin deficiency and excess counter-regulatory hormones ( - Five biochemical investigations (5 marks - 1 mark each) - Blood glucose - to confirm hyperglycemia and monitor treatment - Serum/urine ketones (beta-hydroxybutyrate preferre - - to confirm ketonemia/ketonuria - Arterial blood gas analysis - to assess acid-base status (pH, bicarbonate, pCO2) - Serum electrolytes (Na+, K+, Cl-) - to calculate anion gap and monitor electrolyte imbalances - Serum urea and creatinine - to assess renal function and hydration status ( - Biochemical basis for acid-base disturbance (3 marks) - Insulin deficiency leads to increased lipolysis and fatty acid oxidation in the liver - This produces excessive ketone bodies (acetoacetate, beta-hydroxybutyrate, and aceton - - Ketone bodies are organic acids that accumulate in blood, causing metabolic acidosis with high anion gap - Compensatory respiratory alkalosis occurs through hyperventilation (Kussmaul breathing) to eliminate CO2 ---
Answer: 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 - - Myoglobin ( - Time course and clinical significance of troponin (4 marks) - Troponins begin to rise 3-4 hours after myocardial injury - Peak levels occur at 12-24 hours post-infarction - Remain elevated for 7-14 days (troponin I) or up to 21 days (troponin T) - Clinical significance: High sensitivity and specificity for myocardial injury; useful for early diagnosis, risk stratification, and detecting reinfarction - Serial measurements improve diagnostic accuracy ( - Two other conditions causing troponin elevation (2 marks - 1 mark each) - Acute pulmonary embolism - Chronic kidney disease/renal failure (Accept: myocarditis, heart failure, sepsis, severe hypertension, cardiac traum - ---
Answer: 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) ( - Expected laboratory findings in primary hypothyroidism (3 marks) - Elevated TSH (>4.5 mIU/L) - Low Free T4 (<12 pmol/L) - Low Free T3 - May have positive thyroid antibodies (TPO, thyroglobulin antibodies) indicating autoimmune thyroiditis (Hashimoto's diseas - ( - Differentiation between primary and secondary hypothyroidism (3 marks) Primary Hypothyroidism: - Elevated TSH, Low T4 and T3 - Problem is in the thyroid gland itself Secondary Hypothyroidism: - Low or normal TSH, Low T4 and T3 - Problem is in the pituitary gland (reduced TSH secretion) The key differentiator is TSH level: high in primary, low/normal in secondary ---
Answer: 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: 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 ( - Four biochemical investigations for hypercalcemia (4 marks - 1 mark each) - Serum parathyroid hormone (PTH) - Serum phosphate - Serum albumin (to calculate corrected calcium) - 25-hydroxyvitamin D levels (Accept: alkaline phosphatase, serum protein electrophoresis, urea and creatinin - ( - Biochemical findings in primary hyperparathyroidism (3 marks) - Elevated or inappropriately normal PTH in the presence of hypercalcemia - Low serum phosphate (due to increased renal phosphate excretion) - Elevated alkaline phosphatase (if bone involvement) - May have elevated 1,25-dihydroxyvitamin D - Increased urinary calcium excretion ( - Three complications of prolonged hypercalcemia (3 marks - 1 mark each) - Nephrolithiasis (kidney stones) and nephrocalcinosis - Cardiac arrhythmias and shortened QT interval - Neurological symptoms (confusion, lethargy, com - (Accept: peptic ulcer disease, pancreatitis, bone disease, constipation) ---
Answer: 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 - Jaundice: Excessive breakdown of red blood cells - Example: Sickle cell disease, hemolytic anemia, malaria - Hepatic (Hepatocellular) Jaundice: Dysfunction of hepatocytes affecting bilirubin metabolism - Example: Viral hepatitis, cirrhosis, Gilbert's syndrome - Post-hepatic (Obstructive/Cholestati - Jaundice: Obstruction of bile flow in biliary tree - Example: Gallstones, pancreatic cancer, biliary stricture ( - Type of jaundice and justification (4 marks) Type: Hepatocellular (Hepati - Jaundice (1 mark) Justification (3 marks): - Markedly elevated transaminases (ALT 350, AST 320 U/L) indicate hepatocellular injury - Both conjugated and unconjugated bilirubin are elevated with predominantly unconjugated (mixed pattern) - Alkaline phosphatase is only mildly elevated (not markedly raised as in cholestasis) - Pattern consistent with acute hepatitis (likely viral or drug-induce - ---
Answer: 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- - - Very Low-Density Lipoprotein Cholesterol (VLDL- - or calculated as non-HDL cholesterol ( - Classification and atherogenic potential (5 marks) Classification by density (2 marks): - Chylomicrons (lowest density) - VLDL (very low density) - LDL (low density) - HDL (high density) Atherogenic potential (3 marks): Atherogenic (Pro-atherogenic): - LDL cholesterol - primary atherogenic lipoprotein, deposits cholesterol in arterial walls - VLDL - carries triglycerides, remnants are atherogenic - Associated with increased cardiovascular risk Anti-atherogenic (Protective): - HDL cholesterol - "good cholesterol" - Involved in reverse cholesterol transport (removes cholesterol from tissues to liver) - Higher levels associated with lower cardiovascular risk ---