Alkaline phosphatase isoenzyme patterns in hyperthyroidism

15 Of 36 hyperthyroid patients had elevations in serum alkaline phosphatase activity. There was no difference in mean thyroxine (T₄), triiodothyronine (T₃), age, or duration of illness between the groups with high alkaline phosphatase and normal alkaline phosphatase levels. After treatment, serum alkaline phosphatase levels rose as T₄ levels declined; at 3 months, the mean serum alkaline phosphatase value rose from 7.1 Bodansky units to 10.3 Bodansky units (P <0.005), while the mean T₄ value fell from 18 μg/dl to 7.2 μg/dl (P <0.005). In some patients, serum alkaline phosphatase values have remained elevated for more than 1 year, despite continued normality in thyroid variables. Before therapy, isoenzyme patterns analyzed by polyacrylamide gel electrophoresis were qualitatively normal. As therapy was instituted, the isoenzyme patterns changed markedly, with increased amounts of bone alkaline phosphatase appearing in the serum as T₄ levels were declining and total alkaline phosphatase was rising. Thyroid tissue homogenates from patients with Graves' disease were found to have very low levels of alkaline phosphatase activity and an isoenzyme pattern quite distinct from that in the serum.