Chapter 22-9: Thiazide-Induced Hypercalcemia

TEXTBOOK PRESENTATION

Thiazide diuretics cause mild hypercalcemia. This hypercalcemia is associated with a normal or elevated PTH 98% of the time.

DISEASE HIGHLIGHTS

1. Thiazide diuretics cause hypocalciuria.

   1. Sodium depletion causes increased sodium and calcium retention in the proximal tubule.

   2. Thiazides probably also augment the renal effect of PTH.

2. Thiazide-induced hypercalcemia has traditionally thought to be mild and short-lived because in response to the hypocalciuria-induced hypercalcemia, PTH secretion is suppressed, normalizing calcium levels.

3. A recent study, however, suggests that hypercalcemia is discovered, on average, about 5 years after initiation of therapy.

EVIDENCE-BASED DIAGNOSIS

1. The diagnosis of thiazide-induced hypercalcemia depends on documenting hypercalcemia in a patient taking a thiazide diuretic.

2. Upon discontinuation of thiazide, approximately one-third of patients will have resolution of hypercalcemia.

3. Of the remaining two-thirds, about 80% will be found to have primary hyperparathyroidism.

TREATMENT

A patient with transient hypercalcemia after beginning a thiazide does not need treatment. Those with persistent hypercalcemia after discontinuing therapy should be evaluated for primary hyperparathyroidism.