Clinical Biochemistry Prometric exam questions with answers

1. Question 1Analytical techniques and instrumentationmedium

   A patient with severe hypertriglyceridaemia has sodium 124 mmol/L on the main analyser, which uses indirect ion-selective electrodes. A blood gas analyser gives 139 mmol/L. What explains the difference?

   1. ADirect ISEs are affected by haemolysis
   2. BSodium is lost from the sample by evaporation
   3. CThe blood gas analyser uses flame photometry
   4. DIndirect ISE dilution error from increased lipid volume
   Show answer and explanation▾

   Answer: D. Indirect ISE dilution error from increased lipid volume

   Indirect ISEs dilute the sample and assume normal plasma water content; excess lipid or protein reduces water fraction and causes pseudohyponatraemia. Direct ISEs measure activity in plasma water and are unaffected.

2. Question 2Carbohydrate, lipid and cardiac biochemistryhard

   A patient has a high-sensitivity troponin above the 99th percentile on two samples with no change between them. There are no symptoms or ECG changes of ischaemia. How should this be classified?

   1. AChronic myocardial injury
   2. BAcute myocardial infarction
   3. CAcute non-ischaemic injury
   4. DNormal troponin result
   Show answer and explanation▾

   Answer: A. Chronic myocardial injury

   Myocardial injury is troponin above the 99th percentile upper reference limit; it is acute if there is a rise or fall and chronic if stable. Myocardial infarction requires acute injury plus clinical evidence of ischaemia.

3. Question 3Carbohydrate, lipid and cardiac biochemistrymedium

   A fasting lipid profile shows total cholesterol 6.0, HDL 1.2 and triglyceride 2.2 mmol/L. What is the calculated LDL cholesterol?

   1. A2.6 mmol/L
   2. B4.8 mmol/L
   3. C3.8 mmol/L
   4. D3.0 mmol/L
   Show answer and explanation▾

   Answer: C. 3.8 mmol/L

   Friedewald in mmol/L: LDL = TC - HDL - TG/2.2 = 6.0 - 1.2 - 1.0 = 3.8 mmol/L. The formula is invalid when triglycerides exceed about 4.5 mmol/L.

4. Question 4Endocrinologymedium

   In an overnight 1 mg dexamethasone suppression test for Cushing syndrome, which morning cortisol result indicates failure of suppression?

   1. ABelow 50 nmol/L
   2. BBelow 20 nmol/L
   3. CAbove 50 nmol/L
   4. DExactly 100 nmol/L only
   Show answer and explanation▾

   Answer: C. Above 50 nmol/L

   A 09:00 cortisol above 50 nmol/L (1.8 microgram/dL) after 1 mg dexamethasone at midnight indicates failure to suppress and needs further testing. Oral oestrogens and enzyme-inducing drugs can cause false positives.

5. Question 5Quality control and method evaluationeasy

   A single internal quality control result falls 3.4 SD above the mean. What should happen under Westgard rules?

   1. AReject the run as a 1-3s violation
   2. BAccept the run as a warning only
   3. CAccept if the next control is in range
   4. DAverage with the previous control
   Show answer and explanation▾

   Answer: A. Reject the run as a 1-3s violation

   A single control exceeding the mean by more than 3 SD violates the 1-3s rejection rule, usually indicating random error, and patient results should not be released until the problem is fixed. The 1-2s rule is the warning rule.

6. Question 6Liver, gastrointestinal and pancreatic functionmedium

   A healthy 22-year-old has mild jaundice during a fasting period. Bilirubin is 45 micromol/L, mostly unconjugated, with normal liver enzymes and no haemolysis. What is the most likely diagnosis?

   1. ADubin-Johnson syndrome
   2. BPrimary biliary cholangitis
   3. CCrigler-Najjar type 1
   4. DGilbert syndrome
   Show answer and explanation▾

   Answer: D. Gilbert syndrome

   Gilbert syndrome causes mild unconjugated hyperbilirubinaemia that rises with fasting or illness, with normal enzymes and no haemolysis. Dubin-Johnson causes conjugated hyperbilirubinaemia, and Crigler-Najjar type 1 presents with severe neonatal jaundice.

7. Question 7Quality control and method evaluationhard

   A laboratory is establishing a new reference interval by the non-parametric method. What is the recommended minimum number of healthy reference individuals?

   1. A20 individuals
   2. B120 individuals
   3. C40 individuals
   4. D60 individuals
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   Answer: B. 120 individuals

   CLSI recommends at least 120 reference individuals per partition to estimate the 2.5th and 97.5th percentiles non-parametrically. Twenty samples are used for verifying, not establishing, a transferred interval.

8. Question 8Renal function, electrolytes and acid-baseeasy

   A patient has sodium 140, chloride 100 and bicarbonate 24 mmol/L. What is the anion gap?

   1. A40 mmol/L
   2. B64 mmol/L
   3. C8 mmol/L
   4. D16 mmol/L
   Show answer and explanation▾

   Answer: D. 16 mmol/L

   Anion gap = Na - (Cl + HCO3) = 140 - 124 = 16 mmol/L. Adding potassium changes the result, so laboratories should state which formula they use.

9. Question 9Pre-analytical factors, laboratory safety and ethicsmedium

   A potassium of 6.9 mmol/L is found on a ward sample with no haemolysis. What is the correct action?

   1. ARelease it electronically and wait for the ward to see it
   2. BHold the result until the next day's batch
   3. CRepeat the test three times before reporting
   4. DPhone the result to a responsible clinician and document it
   Show answer and explanation▾

   Answer: D. Phone the result to a responsible clinician and document it

   Critical results must be communicated promptly to a responsible clinician by phone, with read-back confirmation and documentation of who received it and when. Electronic release alone may not be seen in time.

10. Question 10Proteins, therapeutic drug monitoring and toxicologymedium

    Serum protein electrophoresis shows a discrete band in the gamma region. What is the next laboratory step?

    1. AImmunofixation to type the paraprotein
    2. BRepeat electrophoresis in 6 months only
    3. CMeasure C-reactive protein
    4. DMeasure serum albumin
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    Answer: A. Immunofixation to type the paraprotein

    A discrete band suggests a monoclonal paraprotein, which is characterised by immunofixation and quantified, often with serum free light chains. Monitoring without typing misses the diagnosis.

11. Question 11Quality control and method evaluationmedium

    In one run, the level 1 control is 2.2 SD above its mean and the level 2 control is 2.1 SD below its mean. Which rule is violated and what does it indicate?

    1. A2-2s, indicating systematic error
    2. B4-1s, indicating systematic error
    3. CR-4s, indicating random error
    4. D10x, indicating a trend
    Show answer and explanation▾

    Answer: C. R-4s, indicating random error

    A range of more than 4 SD between two controls in the same run violates R-4s and suggests random error, such as pipetting problems or bubbles. The 2-2s rule needs both controls on the same side.

12. Question 12Renal function, electrolytes and acid-basemedium

    A sample shows potassium 9.2 mmol/L, calcium 0.6 mmol/L and very low alkaline phosphatase in a well patient with a normal ECG. What is the most likely cause?

    1. ATrue hyperkalaemia from renal failure
    2. BDelayed separation at low temperature
    3. CContamination with K2EDTA
    4. DHypoparathyroidism with tetany
    Show answer and explanation▾

    Answer: C. Contamination with K2EDTA

    Potassium EDTA contamination raises potassium and chelates calcium, magnesium and the zinc needed for ALP activity, producing this pattern. The sample should be rejected and recollected in the correct order of draw.

13. Question 13Renal function, electrolytes and acid-basemedium

    A bodybuilder with very high muscle mass has a creatinine-based eGFR of 55 mL/min/1.73 m2 but no other evidence of kidney disease. Which test helps confirm true kidney function?

    1. ARepeat creatinine after a meat meal
    2. BCystatin C-based eGFR
    3. CUrine sodium concentration
    4. DSerum urea alone
    Show answer and explanation▾

    Answer: B. Cystatin C-based eGFR

    Creatinine depends on muscle mass and diet, so it can underestimate GFR in muscular people; cystatin C is less affected and is recommended for confirmation. A recent meat meal raises creatinine further.

14. Question 14Renal function, electrolytes and acid-basemedium

    A euvolaemic patient has serum sodium 125 mmol/L and serum osmolality 260 mOsm/kg, with normal thyroid and adrenal function. Which urine findings support SIADH?

    1. AUrine osmolality below 100 and urine sodium below 20
    2. BUrine osmolality above 100 and urine sodium above 30
    3. CUrine osmolality below 50 with high urine volume
    4. DUrine sodium below 10 with high specific gravity
    Show answer and explanation▾

    Answer: B. Urine osmolality above 100 and urine sodium above 30

    SIADH shows inappropriately concentrated urine (osmolality above 100 mOsm/kg) and urine sodium above 30 mmol/L in a euvolaemic patient with hypotonic hyponatraemia. Very dilute urine suggests excess water intake.

15. Question 15Renal function, electrolytes and acid-basemedium

    An arterial gas shows pH 7.50, PaCO2 6.5 kPa and bicarbonate 36 mmol/L. What is the primary disorder?

    1. ARespiratory alkalosis with renal compensation
    2. BMetabolic alkalosis with respiratory compensation
    3. CRespiratory acidosis with renal compensation
    4. DMixed metabolic and respiratory acidosis
    Show answer and explanation▾

    Answer: B. Metabolic alkalosis with respiratory compensation

    Alkalaemia with raised bicarbonate indicates metabolic alkalosis, and the raised PaCO2 reflects compensatory hypoventilation. Respiratory alkalosis would show a low PaCO2.

Last reviewed September 2026. Questions are original and written to the published exam blueprint; they are not taken from any real paper.