Protein level in cerebrospinal fluid; an evaluation of some methods of determination.

HIS STUDY WAS UNDERTAKEN IN AN ATTEMPT to evaluate some of the more promising methods for the determination of cerebrospinal fluid protein with the objective of deciding on the most suitable one for use in this laboratory. There are a number of methods available, with great variations in the ease of performance and the accuracy of results; therefore it seems that some sort of compromise must be made to find a practicable method. We chose the methods for investigation on the basis of two considerations: first, their reported good correlation with results obtained by the Kjeldahl procedure, this method being the one generally accepted for its reliabffity; and second, on sample size required which is a necessary criterion for us, since this laboratory is routinely given a sample of no more than 1 ml. for this determination. A comparative study was made on a series of pooled cerebrospinal fluids, and also on a series of serum and plasma specimens that had been diluted with saline to give protein concentrations in the spinal fluid range. The following methods were used simultaneously: microKjeldahl; the tyrosine equivalence method of Johnston and Gibson; the sulfosalicylic acid method; the trichloroacetic acid method run at 370; and two biuret procedures. The tyrosine equivalence method of Johnston and Gibson (1) has had very favorable reports from nearly every source, the main objec-