Cerebrospinal fluid: electrophoresis and methods for determining immunoglobulin G compared

We describe the use of a microconcentrator membrane with a 10,000 dalton cutoff for treating cerebrospinal fluid (CSF) specimens before electrophoresis. We also examine immunochemical methods based on radial immunodiffusion, rate nephelometry, and nephelometry at quasi-equilibrium for quantifying IgG in CSF by studying calibrator crossover, imprecision at low IgG levels, and patient correlation. Calibrator crossover studies showed that values for all standard materials agreed well with assigned. At IgG quantities lower than 30.0 mg/L, we found the radial immunodiffusion (RID) method difficult to use; the rate and quasi-equilibrium methods were reliable to 11.2 and 3.0 mg/L, respectively. Above their respective cutoffs, correlation studies revealed that all three methods compared well. We performed IgG quantification and protein electrophoresis on 40 CSF specimens from patients having non-neurologic disease, finding normal reference intervals which generally agreed with those established previously; however, the albumin, beta, and gamma electrophoretic fractions we observed differed from those reported previously.