MLT GlobeChemistry: Proteins & electrophoresis – page 7
125 Chemistry MCQs on Proteins & electrophoresis with answers and explanations.
Serum electrophoresis of a healthy adult shows the albumin band split into two equal peaks; other fractions are normal. The most likely explanation is:
Bisalbuminemia is a double albumin band caused by a genetic variant with different charge, and is usually of no clinical importance. It can rarely be acquired, for example with high-dose beta-lactam drugs.
A tall boy with dislocated lenses, learning difficulty and venous thrombosis has very high plasma total homocysteine and high methionine. Which enzyme is most likely deficient?
Classic homocystinuria (CBS deficiency) blocks homocysteine conversion to cystathionine, so both homocysteine and methionine rise. In MTHFR deficiency methionine is low or normal.
A patient with stage 4 chronic kidney disease and no evidence of plasma cell disease has a serum free kappa/lambda ratio of 2.1. The best interpretation is:
Kappa is cleared faster by the kidney than dimeric lambda, so in renal failure both rise and the ratio increases. A renal reference range of about 0.37–3.1 is used instead of 0.26–1.65.
A patient with known kappa light chain myeloma has a free kappa result far lower than expected, but it rises greatly when the sample is re-run at a higher dilution. The cause is:
In immunonephelometry, very high antigen saturates the antibody and forms fewer large complexes, giving falsely low results. Dilution restores the correct antigen–antibody ratio.
In capillary electrophoresis immunosubtraction, serum is incubated with anti-IgG and anti-kappa beads in separate runs. The M-peak disappears in both runs. The M-protein is:
The beads remove proteins that carry the matching heavy or light chain, so the peak vanishes only with the correct antisera. Loss with both anti-IgG and anti-kappa identifies IgG-kappa.