Evidence for secondary hyperparathyroidism in idiopathic hypercalciuria

Area of Science:

• Nephrology
• Endocrinology
• Calcium Metabolism

Background:

• Idiopathic hypercalciuria (IH) is a condition characterized by high urinary calcium excretion without a known cause.
• The relationship between IH and parathyroid hormone (PTH) levels, particularly secondary hyperparathyroidism, remains incompletely understood.

Purpose of the Study:

• To investigate the role of parathyroid hormone (PTH) in idiopathic hypercalciuria (IH).
• To explore the effects of thiazide and furosemide on PTH levels in patients with IH and healthy subjects.

Main Methods:

• Measured circulating immunoreactive parathyroid hormone (PTH) in 40 patients with IH before and during thiazide treatment.
• Administered furosemide to four normal subjects to induce hypercalciuria and measured PTH levels.

Main Results:

• 26 patients with IH had elevated PTH levels; PTH normalized with thiazide treatment.
• Furosemide-induced hypercalciuria in normal subjects elevated PTH levels similarly to those seen in IH patients.
• Thiazide did not increase serum calcium, and alimentary calcium hyperabsorption was ruled out as a cause for high PTH in IH.

Conclusions:

• IH with elevated PTH is likely secondary hyperparathyroidism, not primary hyperparathyroidism or alimentary hyperabsorption.
• A primary renal defect in calcium handling is a plausible cause for IH and associated secondary hyperparathyroidism.