The influence of thiazide intake on calcium and parathyroid hormone levels in patients with primary hyperparathyroidism

ObjectiveThe effects of thiazide medication in patients with primary hyperparathyroidism (PHPT) have so far not been elucidated. The aim of this study was to analyse the extent to which the administration of thiazides may influence biochemical parameters and therefore the diagnosis of PHPT in a large cohort of patients. Design and patientsThe biochemical parameters of 1066 patients with PHPT were analysed, and drug history was documented. Calcium (Ca)/creatinine clearance ratio (CCCR) was calculated. The results of patients given thiazides (n = 170) and those not given thiazides (n = 896) were analysed and compared. MeasurementsTwenty-four-hour urinary calcium excretion (24hU), albumin-corrected serum calcium, PTH, creatinine, 1,25OH- and 25OH-vitamin D were measured, and CCCR was calculated. Results24hU(Ca) and CCCR were significantly lower in patients on thiazides (P = 002 and P = 00068, resp.), and serum creatinine was significantly higher in those subjects (P < 00001). Serum Ca levels only proved different in an analysis of covariance among patients younger than 60 years (P = 0003). Nevertheless, PTH was not different in both groups (P = 0917). ConclusionsAccording to recently published guidelines, 24hUCa measurement is necessary to give indication for surgery in asymptomatic patients and to distinguish between PHPT and familial hypocalciuric hypercalcaemia [FHH]. Thiazides significantly decrease 24hU(Ca), yet neither increase serum Ca nor influence PTH levels in patients with PHPT. However, discontinuing thiazides is crucial for a correct CCCR calculation to pre-operatively rule out FHH. As a consequence, the withdrawal of thiazide medication must be recommended for the diagnosis of PHPT prior to surgery.