Reference Intervals for 24-Hour Urinary Calcium Excretion and Its Association With Bone Metabolism: A Multicenter Study.

Context: The 24-hour urinary calcium excretion (UCaE) not only serves as an important indicator of calcium metabolism balance but also correlates with metabolic diseases. However, the distribution of 24-hour UCaE and its relationship with bone metabolism are unknown.

Objective: To investigate the distribution of 24-hour UCaE and its association with bone metabolism.

Methods: In this multicenter cross-sectional study, 1239 participants underwent physical examinations at 9 tertiary hospitals. Multivariate linear regression was used to explore bone metabolism associated with 24-hour UCaE. The relationship of bone metabolism with 24-hour urinary calcium excretion/urinary creatinine (UCaE/Ucr) was analyzed by using restrictive cubic splines fitting multiple linear regression model.

Results: The 24-hour UCaE median range was 2.27 mmol overall, 2.24 mmol in men, and 2.28 mmol in women. For men, the highest 24-hour UCaE/Ucr was observed in those aged between 30 and 44 years (median: 0.70), whereas the lowest was found aged between 18 and 29 years (median: 0.46). For women, the 24-hour UCaE/Ucr showed a gradual increase with advancing age. In the adjusted model, 24-hour UCaE/Ucr was independently positively associated with 25(OH)D in both men (P = .032) and women (P < .001). It was independently associated with parathyroid hormone (PTH) (P = .031), type Ⅰ collagen-containing cross-linked C-telopeptide (β-CTX) (P = .021) and procollagen type I N-propeptide (P1NP) (P = .048) in men, but not in women. The prevalence of hypercalciuria was 11.6% (men 7.5%; women 14.0%) and significantly varied across age groups and regions (P < .05).

Conclusion: This study established reference intervals for 24-hour UCaE in the Chinese population. This study found gender differences in the relationship between 24-hour UCaE and bone metabolism.