Quantification of Serum Inorganic Phosphorus, Phosphatase, and Urinary Phosphate without Preliminary Treatment

A direct method has been devised for determining serum and urinary inorganic phosphorus and serum phosphatase activity. Inorganic phosphorus forms a phosphomolybdate complex in the presence of borate. The complex is reduced with ascorbic acid. The resulting suspension is solubilized with carbonate and the absorbance measured at 720 nm. Samples containing low to moderate concentrations of bilirubin may be assayed by the method, and it compares favorably with a p-semidine reduction procedure with use of a TCA filtrate. Alkaline phosphatase values obtained by the method in which a β-glycerophosphate substrate is used compare favorably with a reference method in which p-nitrophenolphosphate is used as a substrate. Citrates, fluorides, nitrites, oxalates, and mannitol do not appreciably affect results obtained by the method.