Table 1. CSF Proteinand NephelosReadingComparedfor Five Pooled HumanSera with DifferentAlbumin/GlobulinRatios

CLINICAL CHEMISTRY, Vol. 25, No. 4, 1979 643 fled by adding a precalibrated CSF protein scale, generated by use of a diluted commercial lyophilized qualitycontrol serum. We investigated the validity of using lyophilized materials to construct a precalibrated scale for this nephelometric assay. We found that analyses of serial dilutions of quality-control sera showed a linear relationship between nephelometric reading and total protein; however, for different quality-control sera the slope of the line varied. We also investigated dilute human serum, which has been recommended for use as a standard (2, 3), but analyses of dilutions of pooled normal human serum of differing total protein and albumin content gave results similar to those obtained with the quality-control sera (Table 1). Evidently results obtainable by the nephelometric method are a function of the calibration material used to generate the scale. It has been well documented that the results obtained for tUrbidimetric methods of CSF total protein estimation with sulfosalicylic acid depend on the albumin/globulin ratio (3-5). We have shown (Table 1) that if the albumin/globulin ratio of the standard material differs from 1.0 to 1.47, a 20% difference in CSF total protein results. We consider that there are serious problems of accuracy associated with methods of standardization, both within an individual laboratory and between laboratories. A particular problem may lie in the assay of successive fluids from the individual patients whose CSF albumin/globulin ratios may be expected to alter as recovery ensues. We therefore consider that the nephelometric method for estimation of CSF total protein is not to be recommended for routine laboratory use.