Sialic acid in human serum and cerebrospinal fluid. Comparison of methods and reference values

Sialic acid was estimated simultaneously by three methods: chemical determination based on Warren's method (Meth. Enzymol. 6, 463-464 (1963) with slight modifications, enzymatic measurement with a commercially available test kit, and high performance liquid chromatography (HPLC) according to Silver et al. (J. Chromatogr. 224, 381-388 (1981). These methods showed closely correlated (r greater than 0.930) results and displayed similar precision data. Interference studies demonstrated sufficient specificity for the chemical assay, which was 5-6 times more sensitive than the enzymatic test and hence chosen for the establishment of reference values. From 249 sera from healthy people between 16 and 63 years the 0.025-0.975-reference intervals were calculated to be 1.57-2.63 mmol/l for 127 men, and 1.69-2.64 mmol/l for 122 women with no significant dependence on age and sex. From 43 cerebrospinal fluids from healthy adults the respective values were 17.3-50.4 mumol/l. These data correspond to those of the literature. Some chemical assays employing thiobarbituric acid were compared. They proved reliable in contrast to the reaction of serum with 4-dimethylaminobenzaldehyde.