A micro-method for measuring total protein in cerebrospinal fluid by using benzethonium chloride in microtiter plate wells.

By using a benzethonium chloride concentration 12-fold that described originally (Clin Chem 1979;25:1317-9), we developed a reliable method suitable for routine measurement of total protein in cerebrospinal fluid. Only 10 microL of sample is required. Reactivity to immunoglobulin G (IgG) and to albumin (Alb) is similar, as is necessary for specimens that can have very varied IgG/Alb ratios. The assay, performed in a microtiter plate for ease of use, has a between-batch coefficient of variation of 3.4% for a protein concentration of 450 mg/L. This contrasts with a dye-binding technique with Ponceau S, for which the CV was 9% at the same concentration.