Photometric determination of sialic acids in serum and cerebrospinal fluid with the thiobarbituric acid method

The specific and sensitive thiobarbituric acid of Warren for sialic (N-acetylneuraminic) acid was modified so as to eliminate the extraction step. Serum total sialic acid values with this procedure were the same as those with the diphenylamine method, whereas the globulin sialic acid levels were elevated by comparison. The globulin sialic acid/total globulin ratio values while significantly elevated in cancer, rheumatoid arthritis, multiple sclerosis, etc., gave the highest results in amaurotic family idiocy (Tay-Sachs' disease). The similarity of the spectral curves obtained for hydrolyzed serum, orosomucoid, the protein-bound fraction of cerebrospinal fluid and for unhydrolyzed N-acetylneuraminic acid provided evidence for a common chromogen. The absence of non-protein-bound or “free” sialic acid in CSF was shown both by spectral and chromatographic analysis. While elevated protein-bound CSF sialic acid values were found in a number of neurological conditions, the normal ratio (sialic acid/total protein) values obtained indicate that this increase reflects that of the total protein.