Disturbances of calcium and magnesium metabolism occur in most hyperthyroid patients.

The concentrations in serum of total and ionised calcium, phosphate, magnesium, albumin and alkaline phosphatase activity were measured in patients when hyperthyroid and again when euthyroid. Significant declines in the mean values of ionised calcium, phosphate and alkaline phosphatase activity and significant increases in the mean concentrations of magnesium and albumin were observed. Similar changes were observed in most individual patients. Levels of ionised calcium greater than two standard deviations (representing between batch imprecision) above the upper limit of the reference range were present in 15.6% of hyperthyroid patients. The hyperthyroid levels of calcium, ionised calcium and alkaline phosphatase activity were highest in patients with the most severe thyrotoxicosis. Disturbances of calcium and magnesium metabolism are frequent in hyperthyroid patients.