Clinical_Biochemistry_20_Scenario_Based_QA_RAG
                     Clinical Biochemistry
20 Scenario-Based Questions and Answers with Explanations
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Use these exam-style clinical scenarios to test your clinical biochemistry knowledge. Read each case, choose the 
best answer, then check the explanation to understand the reasoning. This material is for exam practice and 
education only, not a substitute for clinical guidelines or professional judgment. Reference ranges and units vary 
between laboratories.
Question 1
A 19-year-old with type 1 diabetes presents with vomiting and deep, rapid breathing. Glucose is 28 mmol/L,
ketones are strongly positive, and venous pH is 7.10. Na⁺ is 136, Cl⁻ is 98 and HCO₃⁻ is 8 mmol/L. Which 
acid-base disturbance is present?
A.  Normal anion gap metabolic acidosis
B.  Respiratory acidosis
C.  High anion gap metabolic acidosis
D.  Metabolic alkalosis
Answer: C. High anion gap metabolic acidosis
Explanation: Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻) = 136 − 106 = 30 mmol/L, well above the usual 8 to 16. The 
unmeasured anions are ketoacids, which is typical of diabetic ketoacidosis. The deep breathing (Kussmaul 
respiration) is respiratory compensation, not the primary disorder.
Question 2
A 62-year-old man presents 3 days after an episode of severe chest pain. His ECG is non-diagnostic. Which 
biochemical marker is most useful to confirm recent myocardial infarction?
A.  Cardiac troponin
B.  CK-MB
C.  Myoglobin
D.  AST
Answer: A. Cardiac troponin
Explanation: Cardiac troponin rises within a few hours of myocardial injury and stays elevated for 7 to 14 
days, so it detects late presentations. CK-MB normalizes within about 48 to 72 hours, myoglobin rises early 
but falls within a day and is not cardiac-specific, and AST is no longer recommended.
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Question 3
A 70-year-old man with small cell lung cancer is clinically euvolemic. Serum Na⁺ is 122 mmol/L, serum 
osmolality is 255 mOsm/kg, urine osmolality is 480 mOsm/kg and urine Na⁺ is 55 mmol/L. Thyroid and 
adrenal function are normal. What is the most likely diagnosis?
A.  Psychogenic polydipsia
B.  Diuretic-induced hypovolemic hyponatremia
C.  Adrenal insufficiency
D.  Syndrome of inappropriate ADH secretion (SIADH)
Answer: D. Syndrome of inappropriate ADH secretion (SIADH)
Explanation: Low serum osmolality with inappropriately concentrated urine (above 100 mOsm/kg) and 
urine Na⁺ above 30 mmol/L in a euvolemic patient indicates SIADH, here likely from a tumor. Diagnosis 
requires excluding hypothyroidism, adrenal insufficiency and diuretic use. In psychogenic polydipsia the 
urine is maximally dilute.
Question 4
An asymptomatic outpatient has a potassium of 6.8 mmol/L with a normal ECG and normal renal function. 
The laboratory notes that the sample was hemolyzed and reached the lab after a long delay. What is the 
best next step?
A.  Give IV calcium and insulin-dextrose immediately
B.  Repeat the test on a fresh, non-hemolyzed sample
C.  Arrange urgent dialysis
D.  Start a potassium binder and recheck in a week
Answer: B. Repeat the test on a fresh, non-hemolyzed sample
Explanation: This pattern suggests pseudohyperkalemia: hemolysis, delayed separation, fist clenching, or 
marked thrombocytosis or leukocytosis release potassium in vitro. A fresh, properly handled sample should 
be taken. Emergency treatment is reserved for patients with ECG changes or a clinical reason to believe the 
result is real.
Question 5
A 45-year-old woman with recurrent kidney stones has an adjusted calcium of 2.85 mmol/L, a low 
phosphate of 0.6 mmol/L and a raised PTH. What is the most likely diagnosis?
A.  Primary hyperparathyroidism
B.  Hypercalcemia of malignancy due to PTHrP
C.  Vitamin D toxicity
D.  Secondary hyperparathyroidism of chronic kidney disease
Answer: A. Primary hyperparathyroidism
Explanation: High calcium with an inappropriately high PTH and low phosphate points to primary 
hyperparathyroidism, usually from a parathyroid adenoma. In malignancy and vitamin D toxicity PTH is 
suppressed, and in secondary hyperparathyroidism calcium is low or normal.
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Question 6
A 50-year-old woman has fatigue, weight gain and cold intolerance. TSH is 28 mIU/L and free T4 is low. 
What is the most likely diagnosis and the most useful follow-up test?
A.  Secondary (pituitary) hypothyroidism; MRI of the pituitary
B.  Graves disease; TSH receptor antibodies
C.  Primary hypothyroidism; anti-thyroid peroxidase antibodies
D.  Non-thyroidal illness; repeat in 3 days
Answer: C. Primary hypothyroidism; anti-thyroid peroxidase antibodies
Explanation: A high TSH with low free T4 indicates primary hypothyroidism, most commonly from 
autoimmune (Hashimoto) thyroiditis, supported by anti-TPO antibodies. In pituitary disease TSH would be 
low or inappropriately normal.
Question 7
A 32-year-old woman has palpitations, weight loss, heat intolerance and exophthalmos. TSH is below 0.01 
mIU/L and free T4 is raised. Which antibody test best supports the likely cause?
A.  Anti-dsDNA antibodies
B.  TSH receptor antibodies
C.  Anti-mitochondrial antibodies
D.  Anti-GAD antibodies
Answer: B. TSH receptor antibodies
Explanation: Suppressed TSH with raised free T4 is thyrotoxicosis, and with eye signs the cause is Graves 
disease, driven by stimulating TSH receptor antibodies. Anti-TPO antibodies may also be present but are 
less specific.
Question 8
A patient has jaundice, pale stools, dark urine and itching. ALP is 650 U/L, GGT is markedly raised, ALT is 80 
U/L, and bilirubin is mainly conjugated. Which pattern does this represent?
A.  Hemolytic jaundice
B.  Hepatocellular injury
C.  Gilbert syndrome
D.  Obstructive (cholestatic) jaundice
Answer: D. Obstructive (cholestatic) jaundice
Explanation: A disproportionate rise in ALP and GGT with conjugated hyperbilirubinemia, bilirubinuria and 
pale stools indicates cholestasis, for example from gallstones or a pancreatic head tumor. Urinary 
urobilinogen is reduced or absent. Hemolysis and Gilbert syndrome cause unconjugated hyperbilirubinemia
without bilirubinuria.
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Question 9
A man with heavy alcohol intake has AST 180 U/L, ALT 70 U/L, GGT 450 U/L and MCV 108 fL. Which finding 
best supports alcohol-related liver disease?
A.  AST:ALT ratio above 2 with markedly raised GGT
B.  ALT far higher than AST, in the thousands
C.  Isolated raised ALP
D.  Normal GGT
Answer: A. AST:ALT ratio above 2 with markedly raised GGT
Explanation: In alcoholic liver disease AST usually exceeds ALT (ratio above 2), GGT is raised and MCV is 
often increased. Enzyme levels are rarely above 300 U/L. Very high transaminases with ALT dominant 
suggest viral or ischemic hepatitis or drug toxicity.
Question 10
A patient with gallstones has epigastric pain radiating to the back and repeated vomiting. Which test is the 
most useful for diagnosing acute pancreatitis?
A.  ALT
B.  Creatine kinase
C.  Serum lipase
D.  Serum LDH
Answer: C. Serum lipase
Explanation: Serum lipase above 3 times the upper reference limit is the preferred test, as it is more 
specific than amylase and stays raised longer. Amylase can rise in salivary gland disease, macroamylasemia 
and other abdominal conditions. ALT above about 150 U/L supports a gallstone cause.
Question 11
An 80-year-old cachectic woman has a creatinine of 60 µmol/L (0.68 mg/dL), but her clinicians suspect 
reduced kidney function. Which test is a useful alternative for estimating GFR?
A.  Serum urea
B.  Serum cystatin C
C.  Serum uric acid
D.  Urine specific gravity
Answer: B. Serum cystatin C
Explanation: Creatinine depends on muscle mass, so a low-normal value can hide a reduced GFR in frail or 
cachectic patients. Cystatin C is produced by all nucleated cells and is less affected by muscle mass, 
although thyroid disease, steroids and inflammation can influence it.
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Question 12
A 28-year-old has periorbital edema. A 24-hour urine collection contains 5 g of protein and serum albumin 
is 20 g/L. Which additional finding is most expected?
A.  Low total cholesterol
B.  High serum albumin
C.  Red cell casts as the defining feature
D.  Raised cholesterol with lipiduria
Answer: D. Raised cholesterol with lipiduria
Explanation: This is nephrotic syndrome: proteinuria above 3.5 g/24 h, hypoalbuminemia and edema. Low 
oncotic pressure stimulates hepatic lipoprotein synthesis, causing hyperlipidemia and lipiduria. Loss of 
antithrombin raises thrombosis risk. Red cell casts point to nephritic disease.
Question 13
A 30-year-old woman with heavy periods has Hb 8.5 g/dL, MCV 68 fL, ferritin 6 µg/L, raised TIBC and low 
transferrin saturation. What is the most likely diagnosis?
A.  Iron deficiency anemia
B.  Anemia of chronic disease
C.  Thalassemia trait
D.  Sideroblastic anemia
Answer: A. Iron deficiency anemia
Explanation: Low ferritin is the most specific marker of depleted iron stores, and raised TIBC with low 
saturation confirms iron deficiency. In anemia of chronic disease ferritin is normal or high and TIBC is low or
normal. Thalassemia trait has normal ferritin.
Question 14
A 60-year-old vegan has macrocytic anemia and tingling in the feet. Both methylmalonic acid (MMA) and 
homocysteine are raised. What is the most likely diagnosis?
A.  Folate deficiency
B.  Hypothyroidism
C.  Vitamin B12 deficiency
D.  Iron deficiency
Answer: C. Vitamin B12 deficiency
Explanation: B12 deficiency raises both MMA and homocysteine, while folate deficiency raises 
homocysteine but leaves MMA normal. Neurological symptoms also favor B12 deficiency. Treating with 
folate alone can improve the anemia but allow neurological damage to progress.
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Question 15
A fasting lipid profile shows total cholesterol 9.0 mmol/L, HDL-C 1.0 mmol/L and triglycerides 6.5 mmol/L. 
What is the best approach to LDL-C?
A.  Report the Friedewald-calculated LDL-C
B.  Measure LDL-C directly (or use a validated alternative equation)
C.  Report only HDL-C
D.  Report total cholesterol only
Answer: B. Measure LDL-C directly (or use a validated alternative equation)
Explanation: The Friedewald equation (LDL-C = TC − HDL-C − TG/2.2 in mmol/L) becomes unreliable when 
triglycerides exceed about 4.5 mmol/L (400 mg/dL). Direct measurement or another validated method 
should be used, and secondary causes such as diabetes, hypothyroidism and alcohol should be considered.
Question 16
A 40-year-old with chronic hemolytic anemia has polyuria and polydipsia. HbA1c is 5.2% (33 mmol/mol), 
but a random plasma glucose is 18 mmol/L. What is the most appropriate interpretation?
A.  Diabetes is excluded because HbA1c is normal
B.  Repeat HbA1c in 6 months
C.  HbA1c is more reliable than glucose in this patient
D.  HbA1c is likely falsely low; diagnose using plasma glucose criteria
Answer: D. HbA1c is likely falsely low; diagnose using plasma glucose criteria
Explanation: Shortened red cell survival, recent transfusion or some hemoglobin variants can make HbA1c 
falsely low. A random glucose of 11.1 mmol/L (200 mg/dL) or higher with classic symptoms is diagnostic. 
Fructosamine can help monitor control when HbA1c is unreliable.
Question 17
A 35-year-old woman with weight gain, striae and hypertension undergoes a 1 mg overnight 
dexamethasone suppression test. Her 8 AM cortisol is 280 nmol/L (normal suppression is below 50 nmol/L).
How should this be interpreted?
A.  Failure to suppress; consistent with Cushing syndrome and needs confirmation
B.  Normal suppression
C.  Consistent with Addison disease
D.  Cushing syndrome is excluded
Answer: A. Failure to suppress; consistent with Cushing syndrome and needs confirmation
Explanation: Failure to suppress cortisol suggests endogenous hypercortisolism. Confirmation uses 24-hour 
urinary free cortisol or late-night salivary cortisol, followed by ACTH measurement to find the cause. Oral 
estrogens, obesity, depression and enzyme-inducing drugs can give false positives.
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Question 18
A 40-year-old has episodes of headache, sweating and palpitations with severe hypertension. Which is the 
best biochemical screening test for the suspected tumor?
A.  Urinary 5-HIAA
B.  Plasma renin activity
C.  Plasma free metanephrines or 24-hour urinary fractionated metanephrines
D.  Serum cortisol
Answer: C. Plasma free metanephrines or 24-hour urinary fractionated metanephrines
Explanation: The picture suggests pheochromocytoma. Metanephrines, the metabolites of catecholamines,
are the most sensitive screening tests because tumors release them continuously. Urinary 5-HIAA is used 
for carcinoid tumors, and medications such as tricyclics and some antihypertensives can interfere.
Question 19
In a laboratory, ten consecutive internal quality control results for a glucose assay all fall on the same side 
of the mean, though none exceeds 2 SD. How should this be interpreted?
A.  Random error; reject the run
B.  Systematic error (shift or trend); investigate calibration and reagents
C.  Acceptable performance; no action needed
D.  Out of control only if a value exceeds 3 SD
Answer: B. Systematic error (shift or trend); investigate calibration and reagents
Explanation: A run of consecutive controls on one side of the mean (the 10x rule in the Westgard system) 
signals a systematic error, such as calibration drift or reagent deterioration. Random errors typically cause 
single large deviations such as a 1-3s violation.
Question 20
A 25-year-old with prolonged vomiting has pH 7.52, HCO₃⁻ 38 mmol/L, K⁺ 2.9 mmol/L and Cl⁻ 82 mmol/L. 
What is the expected acid-base disorder?
A.  Hyperchloremic normal anion gap acidosis
B.  Respiratory alkalosis
C.  High anion gap metabolic acidosis
D.  Hypochloremic, hypokalemic metabolic alkalosis
Answer: D. Hypochloremic, hypokalemic metabolic alkalosis
Explanation: Loss of gastric hydrochloric acid and volume depletion cause metabolic alkalosis with low 
chloride and potassium. Urinary chloride is typically low (below 20 mmol/L), which marks it as chloride-
responsive. Treatment is saline and potassium replacement.
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