Morning urinary calcium/creatinine ratio as a sex-specific screening tool for detecting hypercalciuria in hypoparathyroidism.

BACKGROUND

Hypercalciuria is a relevant complication in patients with treated hypoparathyroidism. While hypercalciuria is usually estimated by 24-hour urinary calcium excretion (24hUCa), the calcium/creatinine ratio (CaCrR) of a morning urine sample is more often used in pediatric endocrinology due to feasibility. This study aims to compare these two approaches in adult patients with hypoparathyroidism.

METHODS

In a cohort of 184 systematically evaluated patients with primary hypoparathyroidism (93 % postoperative, 73 % female), the 24hUCa was compared with the CaCrR of a morning spot urine at home. All patients were evaluated at two University hospitals.

RESULTS

60 % of patients met the sex-specific targets of 24hUCa (<6.25 mmol/d for female, < 7.50 mmol/d for men). CaCrR of spot urine correlated significantly with 24hUCa (r = 0.59, p < 0.001). Despite no significant differences between sexes in serum calcium and 24hUCa, females showed significantly higher CaCrRs than men (0.41 vs. 0.29; p = 0.005) due to lower creatinine levels (p < 0.001). ROC-analysis revealed that a CaCrR cutoff of 0.31 mmol/mmol correctly identified hypercalciuria in men with a sensitivity of 83.3 % and a specificity of 82.1 % (AUROC 0.87, PPV=0.75, NPV=0.89). In females, a cutoff of 0.25 mmol/mmol showed high sensitivity (83.3 %), but low specificity (64.6 %) for detecting hypercalciuria (NPV=0.88, PPV=0.57).

CONCLUSION

We propose a CaCrR cut-off of 0.31 mmol/mmol as surrogate for hypercalciuria in male patients. For female patients, the CaCrR does not reliably distinguish between patients with and without hypercalciuria, but a cut-off of 0.25 mmol/mmol can be used as screening tool for performing a 24-hour urinary sampling.