DHA Clinical Biochemistry exam questions

6 worked Clinical Biochemistry practice questions

Original exam-style questions from the bank, spread across the blueprint domains. They are not real or recalled exam questions. Try each one, then open the answer for the rationale and reference. None of them appear in the free mock exam, so reading them will not spoil it.

1. Question 1 · Analytical techniques and instrumentation

   A patient taking high-dose biotin supplements has a raised free T4 and a suppressed TSH on streptavidin-biotin immunoassays but no symptoms. What is the most likely explanation?

   1. ATrue Graves disease requiring antithyroid drugs
   2. BBiotin interference with streptavidin-based assays
   3. CHeterophile antibodies raising every result
   4. DThyroid hormone resistance syndrome
   Show answer and explanation

   Correct answer: B. Biotin interference with streptavidin-based assays

   Excess biotin blocks streptavidin binding, giving falsely high results in competitive assays such as free T4 and falsely low results in sandwich assays such as TSH, mimicking hyperthyroidism. Stopping biotin before re-testing or using another platform resolves it.

   Reference: Tietz Textbook of Laboratory Medicine, 7th ed.

2. Question 2 · Endocrinology

   Which thyroid function pattern indicates primary hypothyroidism?

   1. AHigh TSH, low free T4
   2. BLow TSH, high free T4
   3. CLow TSH, low free T4
   4. DHigh TSH, high free T4
   Show answer and explanation

   Correct answer: A. High TSH, low free T4

   In primary hypothyroidism the failing gland makes less T4 and the pituitary increases TSH. Low TSH with low free T4 suggests secondary (central) hypothyroidism.

   Reference: Tietz Textbook of Laboratory Medicine, 7th ed.

3. Question 3 · Liver, gastrointestinal and pancreatic function

   A patient has raised alkaline phosphatase with a raised gamma-glutamyl transferase and normal calcium. What is the most likely source of the ALP?

   1. ABone osteoblasts
   2. BPlacental tissue
   3. CHepatobiliary tree
   4. DIntestinal mucosa
   Show answer and explanation

   Correct answer: C. Hepatobiliary tree

   A raised GGT alongside ALP indicates a hepatobiliary origin, because GGT is not raised in bone disease. Raised ALP with normal GGT suggests bone, as in Paget disease or growth.

   Reference: Tietz Textbook of Laboratory Medicine, 7th ed.

4. Question 4 · Endocrinology

   A patient has mild hypercalcaemia with an inappropriately normal PTH. The calcium:creatinine clearance ratio is 0.005. What is the most likely diagnosis?

   1. APrimary hyperparathyroidism
   2. BHypercalcaemia of malignancy
   3. CVitamin D intoxication
   4. DFamilial hypocalciuric hypercalcaemia
   Show answer and explanation

   Correct answer: D. Familial hypocalciuric hypercalcaemia

   A calcium:creatinine clearance ratio below 0.01 suggests FHH, caused by inactivating CaSR mutations, which does not need parathyroid surgery. Malignancy and vitamin D excess suppress PTH.

   Reference: Tietz Textbook of Laboratory Medicine, 7th ed.

5. Question 5 · Liver, gastrointestinal and pancreatic function

   A patient without abdominal pain has persistently raised serum amylase with normal lipase. Urine amylase is low. What is the most likely explanation?

   1. AMacroamylasaemia
   2. BAcute pancreatitis
   3. CSalivary gland inflammation
   4. DRenal failure alone
   Show answer and explanation

   Correct answer: A. Macroamylasaemia

   Macroamylase is amylase bound to immunoglobulin, too large to be filtered, so serum amylase is high while urine amylase and the amylase:creatinine clearance ratio are low. Pancreatitis raises lipase and urinary amylase.

   Reference: Tietz Textbook of Laboratory Medicine, 7th ed.

6. Question 6 · Proteins, therapeutic drug monitoring and toxicology

   A lithium level from a patient on stable therapy is reported as 4.5 mmol/L, but she is well with no toxic features. Sampling was 12 hours post-dose. What is the most likely cause?

   1. ASample taken too long after the dose
   2. BHaemolysis lowering the result
   3. CEDTA contamination of the sample
   4. DSample collected into a lithium heparin tube
   Show answer and explanation

   Correct answer: D. Sample collected into a lithium heparin tube

   Lithium heparin tubes contain lithium and can produce falsely high results, so a plain serum tube should be used. A 12-hour post-dose sample is the correct timing.

   Reference: Tietz Textbook of Laboratory Medicine, 7th ed.