Chemical Pathology Exam Paper: Acid-Base, OmpathStudy

Chemical Pathology paper (BPA2103 – Human Pathology III, Tue 7th Dec 2021): SECTION A: MCQs 1. Which would be consistent with respiratory alkalosis? a. pH increased; PCO2 normal; Bicarbonate increased b. pH increased; PCO2 decreased; Bicarbonate normal c. pH decreased; PCO2 normal; Bicarbonate decreased d. pH decreased; PCO2 increased; Bicarbonate normal Answer: b 2. Which of the following laboratory results is consistent with primary hypoparathyroidism? a. Low calcium; high inorganic phosphorus (Pi) b. Low calcium; low Pi c. High calcium; high Pi d. High calcium; low Pi Answer: a 3. Which of the following conditions is associated with hypokalemia? a. Addison's disease b. Hemolytic anemia c. Digoxin intoxication d. Alkalosis Answer: d 4. Which of the following results falls within the diagnostic criteria for diabetes mellitus? a. Fasting plasma glucose of 6.7 mmol/L b. Two-hour postprandial plasma glucose of 8.9 mmol/L c. Two-hour plasma glucose of 10 mmol/L following a 75g oral glucose challenge d. Random plasma glucose of 13.9 mmol/L and presence of symptoms Answer: d 5. The modification of diet in renal disease (MDR D) formula for calculating eGFR requires which four parameters? a. Urine creatinine, serum creatinine, height, weight b. Serum creatinine, age, gender, race c. Serum creatinine, height, weight, age d. Urine creatinine, gender, weight, age Answer: b (not clearly marked in script; b is the standard correct MDRD parameter set) 6. The following conditions cause metabolic alkalosis: a. Excessive antacid ingestion b. Diabetes complications c. Renal failure d. Cardiac disease Answer: a 7. The following are causes of metabolic acidosis EXCEPT: a. Renal failure b. Cardiac failure c. Renal tubular acidosis type IV d. Excessive vomiting Answer: b (marked in script; note vomiting causes alkalosis not acidosis, so also arguably an exception) 8. The following are causes of respiratory alkalosis EXCEPT: a. Salicylate poisoning b. Hysterical over breathing c. Chronic lung disease d. Protracted vomiting Answer: d 9. Fluoride is the anticoagulant used in testing blood for: a. Blood sugar b. Coagulation c. Electrolyte d. CBC Answer: a 10. Regarding the regulation of water excretion, all the following statements are true EXCEPT: a. In the presence of ADH, the collecting duct becomes permeable to water b. In the absence of ADH, the distal nephron is almost impermeable to water c. ADH binds to V2 receptors in the distal nephron to enhance the passive movement of water d. In the thick ascending limb of loop of Henle, sodium and chloride are preferably absorbed without water and hence called the Diluting segment Answer: not marked in script --- SECTION B: Short Answer Questions 1. A 5 month old bottle-fed infant with severe diarrhoea has the following serum biochemistry: Sodium 153 mmol/l (135-145), Potassium 2.2 mmol/l (3.3-5.2), Chloride 116 mmol/l (99-113), Bicarbonate 13 mmol/l (19-29), Urea 7.8 mmol/l (<5.5), Creatinine 40 µmol/l (<45) a. State the likely fluid status of this child? (2 marks) Hypertonic (hypernatremic) dehydration b. State the laboratory values that confirm this state? (3 marks) Elevated serum sodium (153 mmol/l) — indicates water loss exceeding sodium loss Raised urea (7.8 mmol/l) — reflects pre-renal component from volume depletion Hypokalemia and low bicarbonate together with raised chloride — reflect diarrhoeal fluid/electrolyte loss and metabolic acidosis contributing to the dehydrated state 2. A 65 year old presented with visible jaundice, deepening in colour, weight loss, pale stools. Total bilirubin 250 µmol/l (<17), ALT 92 U/l (1-41), AST 87 U/l (1-38), ALP 850 U/l (39-117). a. State 2 differential diagnoses (2 marks) Carcinoma of the head of pancreas (obstructive/malignant biliary obstruction) Cholangiocarcinoma / gallstone causing common bile duct obstruction b. State 3 other investigations that would be helpful and expected result (3 marks) Abdominal ultrasound/CT scan — dilated bile ducts, mass lesion, or stone Serum GGT — markedly elevated (confirms cholestatic/obstructive pattern) Tumour markers (CA 19-9) — elevated in pancreatic/biliary malignancy ERCP/MRCP — may show site and cause of obstruction 3. State 3 endocrine diseases which can lead to secondary diabetes and explain the mechanism in each case. Cushing's syndrome — excess cortisol promotes gluconeogenesis and antagonizes insulin action, causing insulin resistance and hyperglycaemia Acromegaly — excess growth hormone induces insulin resistance in peripheral tissues, reducing glucose uptake Phaeochromocytoma — excess catecholamines inhibit insulin secretion and stimulate glycogenolysis/gluconeogenesis, raising blood glucose 4. List with examples 5 factors that may cause intra-individual variation of laboratory values (5 marks) Diurnal/circadian variation (e.g., cortisol higher in morning, lower at night) Posture (e.g., protein and calcium levels higher standing vs supine) Exercise (e.g., raised creatine kinase after strenu