Clinical Chemistry
Domain focus
Clinical chemistry in this exit exam tests the full testing pathway - patient preparation, specimen collection and transport, calibration, internal quality control, reference intervals and safe interpretation of electrolyte, renal, liver, glucose and lipid results in Cambodian hospital laboratories.
Core rules
- Follow the standard order of draw: blood culture, citrate, serum separator, heparin, EDTA, fluoride-oxalate. EDTA carryover falsely lowers calcium and raises potassium.
- Separate serum or plasma promptly; delays raise potassium and LDH and lower glucose.
- Calibrate before patient testing and run at least two QC levels daily and after major maintenance.
- Report critical results such as glucose <2.5 mmol/L or potassium >6.5 mmol/L by phone with read-back.
- Use SI units and age- and sex-specific reference intervals.
Worked example
A 54-year-old man has Na 132 mmol/L, Cl 98 mmol/L, HCO3 18 mmol/L, glucose 28 mmol/L. Anion gap = 132 - (98 + 18) = 16 mmol/L (reference 8-12). The raised gap with severe hyperglycaemia suggests diabetic ketoacidosis. Corrected sodium = 132 + 0.3 x (28 - 5.5) = 138.8 mmol/L. Report glucose urgently and request ketones and blood gas.
Traps
- Reporting potassium from a haemolysed tube without a comment.
- Calling pseudohypoglycaemia real when a fluoride tube was delayed.
- Mixing mg/dL and mmol/L.
- Ignoring lipaemia or icterus interference flags.