Determination of serum acid and alkaline phosphatase using 4-methylumbelliferyl phosphate

The present report compares the performance of several colorimetric substrates presently employed in clinical laboratories for the determination of serum acid and alkaline phosphatase with that of the fluorogenic phosphatase reagent 4-methylumbelliferyl phosphate. Acid and alkaline phosphatase assays were performed on reference hospital populations in Nigeria and the United States. The results of both acid and alkaline phosphatase determinations indicate that the coefficient of variation is smaller for the fluorometric assay than for the colorimetric methods that employ either phenyl phosphate or p-nitrophenyl phosphate as the substrate. Furthermore, serum acid phosphatase determinations using 4-methylumbelliferyl phosphate identified increased serum enzyme levels in 6/6 cases of prostatic carcinoma and 9/9 cases of Gaucher's disease. The occurrence of elevated serum alkaline phosphatase levels in 24/24 cases involving liver and bone disease was also confirmed by the fluorometric alkaline phosphatase assay. In addition, sera from eight patients with the connective tissue disease, osteogenesis imperfecta, were found to contain normal levels of acid and alkaline phosphatase by the fluorometric assays. From these results it appears that the sensitive and rapid fluorometric assay procedures can be readily employed in the clinical pathology laboratory for the determination of serum acid and alkaline phosphatase levels.