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Egyptian Board Clinical Pathology study materials
Egyptian Board Clinical Pathology study resources

Egyptian Board Clinical Pathology: Chemical Pathology (Clinical Biochemistry)

Egyptian Board Clinical Pathology · Work through your exam, one topic at a time.

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Chemical Pathology (Clinical Biochemistry)

Chemical pathology in this board tests whether you can turn a biochemical result into a defensible clinical interpretation: choosing the right test, knowing pre-analytical limits, applying decision limits rather than reference intervals, and calculating derived values correctly.

Core rules

  • Report reference intervals by age, sex and, for pregnancy, trimester; a value inside the interval is not automatically normal for a symptomatic patient.
  • Creatinine-based eGFR (CKD-EPI) is unreliable in acute kidney injury, extremes of muscle mass, pregnancy and children; do not report an eGFR in evolving AKI.
  • Anion gap = Na − (Cl + HCO3), roughly 8–12 mmol/L; correct for hypoalbuminaemia by adding 2.5 mmol/L per 10 g/L fall in albumin.
  • Corrected sodium in hyperglycaemia: add 1.6 mmol/L per 5.5 mmol/L glucose above 5.5.
  • Corrected calcium = measured Ca + 0.02 × (40 − albumin g/L).
  • Osmolal gap = measured osmolality − (2Na + glucose + urea); a gap above about 10 mosmol/kg suggests an unmeasured osmole such as ethanol, methanol or ethylene glycol.
  • HbA1c reflects 8–12 weeks of glycaemia; interpret cautiously with haemoglobinopathy, recent transfusion, iron deficiency and pregnancy.
  • High-sensitivity troponin is interpreted against the 99th percentile upper reference limit and the serial delta, not a single "high" value.

Worked example

A diabetic patient has Na 128 mmol/L and glucose 28 mmol/L. Corrected Na = 128 + 1.6 × ((28 − 5.5)/5.5) ≈ 128 + 6.5 = 134.5 mmol/L. The measured sodium is dilutional pseudohyponatraemia from hyperglycaemia; the patient is close to normonatraemia and should not be given hypertonic saline on the basis of the uncorrected figure.

Traps

  • Reporting a derived value (eGFR, corrected calcium) without stating the formula and assumptions.
  • Mixing units: mg/dL and mmol/L, creatinine µmol/L and mg/dL.
  • Calling a raised potassium disease when the sample is haemolysed or the tourniquet was prolonged.
  • Treating a mild isolated enzyme rise as a diagnosis instead of repeating it and identifying the pattern (hepatocellular vs cholestatic).