Origin of an elevated plasma alkaline phosphatase activity in non-jaundiced patients.

Samples from 260 non-jaundiced patients with elevated plasma alkaline phosphatase activities were analysed for gamma-glutamyltransferase and 5'-nucleotidase activity, and for alkaline phosphatase isoenzyme pattern. The plasma gamma-glutamyltransferase activity was found to be a more sensitive index than that of plasma 5'-nucleotidase in confirming the presence of a liver component of the elevated plasma alkaline phosphatase. If the gamma-glutamyltransferase level is normal it is probable that the increase in plasma alkaline phosphatase activity is of bone origin. However, and elevated gamma-glutamyltransferase result does not exclude a bone component; in this situation plasma alkaline phosphatase isoenzymes should be estimated. The causes of elevated activities of plasma alkaline phosphatase, 5'-nucleotidase and gamma-glutamyltransferase, found in this investigation were generally the same as those found by other worker. The effect of treatment by drugs on gamma-glutamyltransferase, an inducible enzyme, needs more investigation.