Origin of an Elevated Plasma Alkaline Phosphatase Activity in Non-Jaundiced Patients

Summary Samples from 260 non-jaundiced patients with elevated plasma alkaline phosphatase activities were analysed for γ-glutamyltransferase and 5′-nucleotidase activity, and for alkaline phosphatase isoenzyme pattern. The plasma γ-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 γ-glutamyltransferase level is normal it is probable that the increase in plasma alkaline phosphatase activity is of bone origin. However, an elevated γ-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 γ-glutamyltransferase, found in this investigation were generally the same as those found by other workers. The effect of treatment by drugs on γ-glutamyltransferase, an inducible enzyme, needs more investigation.