Serum inorganic sulphate: quantitation by a new radiochemical method

A new procedure for serum inorganic sulphate determination is described. The method is simple, accurate and highly reproducible. It is based on radioisotopic dilution of 35S-sulphate by protein-free, phosphate-free serum. The decrease in initial 35S-sulphate specific activity (corresponding to added serum sulphate) is determined in the supernatant after partial precipitation of sulphate by barium ion. Serum sulphate is computed thereafter from a standard curve. Recovery of added sulphate from dialysed or undialysed serum was 100%. The intra- and interassay coefficients of variation were 3.5% and 4.1%, respectively. The serum sulphate concentration measured by this method in 93 normal subjects was 400 +/- 90 mumol/l (mean +/- SD), which agreed with the values reported in the literature. Serum sulphate did not correlate with sex (p greater than 0.40, n = 93), but a significant correlation with age was observed (r = 0.25, p less than 0.02, n = 93).