Biochemistry and Clinical Laboratory Sciences
What the exam tests
Biochemistry and Clinical Laboratory Sciences tests metabolic pathways, enzyme kinetics, and the interpretation of common laboratory tests.
Core rules
- Michaelis–Menten: v = Vmax[S]/(Km + [S]). Km is the substrate concentration at half-Vmax; a lower Km means higher apparent affinity. Competitive inhibitors raise apparent Km; noncompetitive inhibitors lower Vmax.
- Glycolysis yields 2 ATP and 2 NADH per glucose; the TCA cycle and oxidative phosphorylation yield most ATP. Uncouplers increase oxygen consumption but reduce ATP synthesis.
- HbA1c reflects average glycemia over roughly 2–3 months. Estimated average glucose in mg/dL = 28.7 × A1c(%) − 46.7.
- Anion gap = Na − (Cl + HCO3); normal is about 8–12 mEq/L. A high gap suggests organic acids, salicylate, methanol, or ethylene glycol.
Worked example
A patient has HbA1c 8.0%. Estimated average glucose = 28.7 × 8.0 − 46.7 = 229.6 − 46.7 = 182.9 mg/dL, about 183 mg/dL. The result is an estimate, not a measured mean, and is unreliable in hemoglobin variants, recent transfusion, or altered red-cell survival. If the fasting glucose is 250 mg/dL but the A1c is 6.5%, look for a discordant condition rather than assuming good control.
Traps
Do not interpret A1c as a fasting glucose; do not use anion gap without checking albumin; do not call an elevated AST specific for liver disease; and do not ignore hemolysis when potassium is spuriously high.