Chemical Pathology Practice Examination

## 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)