Searchable abstracts of presentations at key conferences in endocrinology
Endocrine Abstracts (2023) 97 015 | DOI: 10.1530/endoabs.97.015

BES2023 BES 2023 Section (29 abstracts)

The thiazide challenge test differentiates primary hyperparathyroidism from secondary hyperparathyroidism due to idiopathic hypercalciuria

Verly Ewout 1 , Verroken Charlotte 1 & Lapauw Bruno 1

1Ghent University Hospital - Department of Endocrinology & Metabolic Diseases

Background: Treatment of primary hyperparathyroidism (PHPT) and secondary hyperparathyroidism due to idiopathic hypercalciuria (SHPT-IH) is markedly different. Nevertheless, differentiating one from another remains a challenge and robust diagnostic tools are lacking. The thiazide challenge test (TCT) has been proposed to aid clinicians in their decision making. However, evidence supporting its use is non-existent.

Materials and methods: We performed a retrospective analysis of 25 patients who underwent a TCT at the Ghent University Hospital (Belgium). We assessed serum and urinary samples before and after testing, clinical and imaging outcomes as well as therapy and long-term follow-up to evaluate the efficacy of the TCT. Based on literature, other potentially useful parameters were calculated.

Results: The TCT was considered inconclusive in three cases (12%). PHPT was diagnosed in thirteen (52%), and SHPT in nine (36%) patients. Baseline serum albumin-adjusted calcium (AACa) and serum total calcium (TCa) were similar between patients with PHPT and SHPT-IH. During the TCT, albumin-adjusted calcium (AACa) rose 0,11mmol/l (±0,10) in patients with PHPT and 0,0071mmol/l (±0,10) in patients with SHPT-IH. The change in AACa is significantly different between both groups (one-sided P=0,025). A similar result was found for serum total calcium (TCa), which rose 0,14mmol/l (±0,12) in patients with PHPT compared to 0,012mmol/l (±0,15) in patients with SHPT-IH (one-sided P=0,024). The TCT has a calculated sensitivity of 81,8%, a specificity of 77,8% and a likelihood ratio of 3,68. We observed no differences in serum parathormone (PTH) levels and urinary calcium excretion (UCE) between patients with PHPT and SHPT-IH (101,7ng/l (±26,9) vs. 105,7ng/l (±53,8) and 10,9mmol/24 hours (±3,0) vs. 9,4mmol/24 hours (±3,2) respectively). The calcium-phosphorous ratio (Ca/P), the PTH-inhibition rate (PTH-IR) and the parathyroid function index (PF-index) did not differ significantly between patients with PHPT and SHPT-IH during the TCT. Mean serum potassium levels declined from 4,6mmol/l (±0,4) to 3,8mmol/l (±0,4) during the TCT (P<0,001). No severe hypokalemia (<3,0mmol/l) was observed. Creatinine values did not change significantly during the TCT.

Conclusion: The TCT can aid in discriminating patients with PHPT from those with SHPT-IH based on the rise in serum calcium. It can be easily used in all patients with nephrolithiasis or hypercalciuria, an elevated PTH, and a normal to slightly elevated serum calcium. Notwithstanding mild hypokalemia occurs frequently, we observed no severe side effects. Other variables such as serum PTH, UCE, Ca/P, PTH-IR and PF-index did not differentiate between both groups. Larger prospective trials are necessary to reassess the relevance of different biochemical parameters and the diagnostic potential of the TCT.

Article tools

My recent searches

No recent searches.