Chemical Pathology Practice Examination: OmpathStudy

MBPA 3600 - Year Three MBChB --- INSTRUCTIONS TO CANDIDATES Section A : Short Answer Questions (10 marks each) - Answer ANY TWO questions Section B : Long Essay Questions (20 marks each) - Answer ANY ONE question Time Allowed : 2 hours Total Marks : 40 marks --- SECTION A: SHORT ANSWER QUESTIONS (10 Marks Each) Answer ANY TWO Questions --- QUESTION 1 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. (a) Define diabetic ketoacidosis (DKA). (2 marks) (b) List FIVE biochemical investigations you would request to confirm and manage DKA. (5 marks) (c) Explain the biochemical basis for the acid-base disturbance in DKA. (3 marks) ANSWER TO QUESTION 1 (a) 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 (b) Five biochemical investigations (5 marks - 1 mark each) Blood glucose - to confirm hyperglycemia and monitor treatment Serum/urine ketones (beta-hydroxybutyrate preferred) - 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 (c) 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 acetone) 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 --- QUESTION 2 A 45-year-old man presents with severe chest pain radiating to the left arm. ECG shows ST-segment elevation. (a) Name FOUR cardiac biomarkers used in the diagnosis of acute myocardial infarction. (4 marks) (b) Describe the time course of troponin elevation and its clinical significance. (4 marks) (c) State TWO conditions other than myocardial infarction that can cause troponin elevation. (2 marks) ANSWER TO QUESTION 2 (a) Four cardiac biomarkers (4 marks - 1 mark each) Cardiac Troponin I (cTnI) Cardiac Troponin T (cTnT) Creatine Kinase-MB (CK-MB) Myoglobin (b) 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 (c) 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 trauma) --- QUESTION 3 A 35-year-old woman complains of fatigue, weight gain of 10 kg over 6 months, cold intolerance, and constipation. (a) List FOUR thyroid function tests you would request. (4 marks) (b) Describe the expected laboratory findings in primary hypothyroidism. (3 marks) (c) Differentiate between primary and secondary hypothyroidism based on laboratory results. (3 marks) ANSWER TO QUESTION 3 (a) 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) (b) 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 disease) (c) 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 --- QUESTION 4 Explain the role of the kidney in maintaining acid-base balance. (a) Describe THREE mechanisms by which the kidney regulates acid-base balance. (6 marks) (b) 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 (a) 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 secre