The predictive value of 24-hour urinary calcium for kidney stone risk in primary hyperparathyroidism: insight from a retrospective study of parathyroid adenoma cases.

Background: Primary hyperparathyroidism (PHPT) is associated with an increased risk of kidney stones. However, the clinical utility of 24-hour urinary calcium (24h-UCa) as a predictor of nephrolithiasis, and its role in surgical decision-making, remains uncertain due to inconsistent findings. Objective: To evaluate whether 24h-UCa is a reliable disease-specific predictor of kidney stone risk in patients with PHPT and to identify demographic and biochemical determinants of urinary calcium excretion. Methods: This retrospective study included 306 PHPT patients who underwent curative parathyroidectomy for confirmed adenoma. Demographics, kidney stone history, and biochemical data were collected. T-tests, chi-square tests, multivariate logistic regression, and multiple regression were used to analyze associations of 24h-UCa with kidney stones, demographic, and biochemical indices. Results: Kidney stones were present in 22% of patients. No significant difference in 24h-UCa was observed between stone-formers and non-stone-formers, even after adjustment for age, gender, and race. In contrast, 24h-UCa was significantly higher in men and white patients, with hypercalciuria more prevalent among white individuals. Serum calcium and eGFR were also significantly positively associated with 24h-UCa. Conclusion: Our results suggest that 24h-UCa is not an independent predictor of kidney stone risk in PHPT and is largely influenced by demographic and biochemical factors. Accordingly, routine 24h-UCa measurement for evaluating patients with sporadic PHPT or for guiding parathyroidectomy decisions is not recommended. This study is limited by its retrospective design, reliance on a single urine collection, and lack of detailed dietary or genetic data, which may have introduced variability and reduced power to detect weak associations.