Development and evaluation of an automated dye-binding assay for protein in cerebrospinal fluid

Addition of sodium dodecyl sulfate (SDS) to Coomassie Brilliant Blue reagent equalizes the binding variability of the dye to various proteins and markedly improves the accuracy of quantification of protein in cerebrospinal fluid. In the presence of SDS, the absorption spectrum and the absorption maximum are affected by reaction time and temperature, age of the dye preparation, and protein constituent. I automated this procedure, to optimize precision, enable use of a smaller sample, decrease hands-on time, maintain consistency in the time of reading, and avoid carryover. The results (y) compared well with those of the aca (x), with a Deming de-biased regression equation of y = 0.991x + 14.1 mg/L, Sy.x = 33.4 mg/L. The within-run and between-run precision (CV) was less than 2.5% and less than 4.5%, respectively. Commonly used antibiotics, flucytosine, or amphotericin B do not interfere. This automated procedure is fast and accurate and requires only 10 microL of sample.