Clinical Biochemistry and Laboratory Techniques
Clinical biochemistry measures substances in body fluids to diagnose and monitor disease. This domain tests common analytes, specimen handling, spectrophotometry, chromatography and electrophoresis.
Core rules
- Plasma is obtained with an anticoagulant; serum is the fluid left after clotting.
- Fasting plasma glucose is commonly 70–100 mg/dL (3.9–5.6 mmol/L); higher values need confirmation.
- Blood urea and creatinine reflect kidney function; creatinine is less affected by diet than urea.
- Lipid profiles measure total cholesterol, LDL, HDL and triglycerides; desirable total cholesterol is below 200 mg/dL.
- Liver enzymes ALT and AST indicate hepatocellular damage; ALP is linked to bile ducts and bone.
- Spectrophotometry uses Beer-Lambert law A = εcl. Chromatography separates by partition or adsorption; electrophoresis separates charged molecules by charge and size.
Worked example
A solution gives absorbance 0.45 in a 1 cm cuvette, and ε = 1.5 × 10^4 L mol−1 cm−1. Find concentration. Rearrange A = εcl to c = A/(εl) = 0.45/(1.5 × 10^4 × 1) = 3.0 × 10^−5 M. This calculation assumes the solution obeys Beer-Lambert law and the wavelength is at the absorption maximum.
Traps that cost marks
Haemolysis falsely raises potassium and other analytes. Fasting status must be recorded for glucose and triglycerides. Do not compare a result with a reference range from a different method or unit. A single abnormal value is not a diagnosis; clinical context and repeat testing matter.