Primary hyperparathyroidism and thiazide diuretics.

Six patients receiving thiazide diuretics were referred for evaluation of mild to moderate hypercalcaemia (serum calcium 2.65-2.98 mmol/l). All patients were considered to be suffering from primary hyperparathyroidism. Withdrawal of the diuretic was followed by a reduction in the serum calcium, one patient becoming normocalcaemia. The mechanisms responsible for these changes are discussed. In hypercalcaemic patients taking thiazides, it is recommended that the effects of withholding the diuretic should be observed before more radical measures are considered.