Protein determination in cerebrospinal fluid by protein dye-binding assay

In this study, Coomassie brilliant blue (CBB) and pyrogallol red/molybdate (PRM) protein dye-binding assays for total protein determination in cerebrospinal fluid (CSF) are compared. Using human albumin (HA) as a protein calibrator, protein concentration in CSF samples (n = 73) ranged from 55-1960 mg/L (median: 315 mg/L) with the CBB assay, and from 95-2450 mg/L (median: 395 mg/L) with the PRM assay. Linear regression analysis indicated yCBB = 0.824xPRM - 8 (r = 0.99). The discrepancy between the values was investigated by comparing the response of the two assays to different proteins. Compared with HA, the PRM assay showed a more uniform response to human albumin/globulin (A/G) and bovine gamma globulin (G) than did the CBB assay, but it gave high colour yields with bovine myelin basic protein. When CSF was assayed using A/G as a protein calibrator, agreement between the methods improved (yCBB = 0.960xPRM + 0 [r = 0.99]), indicating that comparability is dictated by the choice of protein calibrator. Of the two assays studied, the PRM assay is recommended for CSF protein determination because it gives a more uniform and linear response to human albumin and globulin over a wider working range.