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Endocrine Abstracts (2023) 90 OC8.3 | DOI: 10.1530/endoabs.90.OC8.3

ECE2023 Oral Communications Oral Communications 8: Calcium and Bone (6 abstracts)

The thiazide challenge test to differentiate between primary hyperparathyroidism and secondary hyperparathyroidism due to idiopathic hypercalciuria.

Ewout Verly 1 , Charlotte Verroken 1 & Bruno Lapauw 1


1UZ Gent (Ghent University Hospital), Endocrinology, Ghent, Belgium

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 as a means to aid clinicians in their decision making. However, evidence supporting its use is scarce.

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 and the calcium load test, other potentially useful parameters were calculated.

Results: Baseline serum albumin-adjusted calcium (AACa) and serum total calcium (TCa) were not significantly different between patients with PHPT and SHPT-IH (2.54 (±0.072) vs 2.55 mmol/l (±0.13) and 2.63 (±0.069) vs 2.64 mmol/l (±0.15) respectively). During the TCT, AACa rose 0.11 mmol/l (±0.10) in patients with PHPT and 0.0071 mmol/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 TCa, which rose 0.14 mmol/l (±0.12) in patients with PHPT compared to 0.012 mmol/l (±0.15) in patients with SHPT-IH (one-sided P=0.024). The TCT can detect PHPT based on an increment in AACa of at least 0.10 mmol/l or in TCa of at least 0.13 mmol/l with a calculated sensitivity of 81.8% and a specificity of 77.8%. Serum parathormone (PTH) levels and urinary calcium excretion (UCE) did not differ between patients with PHPT and SHPT-IH (101.7 ng/l (±26.9) vs 105.7 ng/l (±53.8) and 10.9 mmol/24 hours (±3.0) vs 9.4 mmol/24 hours (±3.2) respectively). PTH levels, UCE, 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.

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. Even though mild hypokalemia occurs frequently, and caution is warranted, no severe side effects were observed. 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.

Volume 90

25th European Congress of Endocrinology

Istanbul, Turkey
13 May 2023 - 16 May 2023

European Society of Endocrinology 

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