A supplement to alkaline phosphatase fractionations: utilization of gamma-glutamyl transpeptidase and hydroxyproline assays

Fractionation of serum alkaline phosphatase by either biochemical or electrophoretic techniques is often insufficient to determine the source of the elevated serum enzyme. In 31 unselected patients with high serum alkaline phosphatase a simultaneous determination of serum gamma glutamyl transpeptidase and urinary hydroxyproline excretion rates was performed, in addition to urea denaturation and L-phenylalanine inhibition tests. Of 25 patients with definite diagnosis, the urea denaturation test correctly identified the source of the elevated serum alkaline phosphatase (ALP) in 16 (64 percent). The serum gamma-glutamyl transpeptidase (GGTP) alone predicted the correct diagnosis in 64 percent of the cases and the urinary hydroxyproline (HOP) alone in 69 percent. When all three tests were performed simultaneously, the combination of results identified the source of the ALP in 88 percent of the cases. It is believed that this combination offers better sensitivity and specificity than any of the three tests used individually.