Tissue sources of elevated serum alkaline phosphatase activity in hyperthyroid patients.

Total alkaline phosphatase (ALP) and its isoenzymes were studied in the sera of 72 hyperthyroid patients and 24 age- and sex-matched controls. Eighty-nine per cent of thyrotoxic patients had elevated total serum ALP activity. Both liver (LALP) and bone (BALP) isoenzymes were present in the sera of 75% of patients. Women (43%) most frequently had elevated levels of LALP and BALP. Men (41%) most often had elevated levels of BALP and normal levels of LALP. The units of BALP present, but not of LALP, were related to measures of thyroid function. Levels of the activity of the aminotransferases and lactic dehydrogenase were usually normal. Gammaglutamyl transferase activity was elevated in nearly 40% of both sexes. The data presented, when correlated with previously reported information, suggest that elevations of serum LALP activity may be due to hepatocellular necrosis with leakage of preformed enzyme into the serum.