Endocrine Abstracts

Background: Hypercalciuria is a relevant complication in patients with treated hypoparathyroidism. Hypercalciuria is usually estimated by 24 h urinary calcium excretion (24 hUCa). In contrast, in pediatric endocrinology the calcium-creatinine-ratio (CaCrR) is more often used due to feasibility. This study aims to compare these two approaches in adult patients with hypoparathyroidism.

Methods: In 181 systematically evaluated patients with primary hypoparathyroidism (93% postoperative, 73% female), the 24 hUCa was compared with the CaCrR of a fasting morning spot urine. All patients were evaluated at two University hospitals.

Results: 60% of patients met the sex-specific targets of 24 hUCa (<6.23 mmol/d for female, <7.51 mmol/d for men). CaCrR of spot urine correlated significantly with 24 hUCa (n=181, r=0.583, P<0.001). Although there were no significant differences between sexes in serum Calcium and 24 hUCa, females showed significant higher CaCrRs than men (0.41 vs 0.28; P=0.02) due to lower creatinine levels (P=0.001). In an ROC-analysis of the CaCrR the cutoff of 0.31 mmol/mmol correctly identified hypercalciuria in men with a sensitivity of 83.3% and a specificity of 86.7% (AUROC 0.88). By contrast, in females the optimal cutoff of 0.31 mmol/mmol only discriminated hypercalciuria from normocalciuria with a sensitivity of 83.3% and a specificity of 64.6% (AUROC 0.82). The negative predictive value for males was 86%. For females it was 64% (cutoff 0.3 mmol/mmol) or 85% (cutoff 0.45 mmol/mmol), respectively.

Conclusion: There are sex-specific differences in CaCrRs between female and male patients with hypoparathyroidism. Only in male patients a cutoff of 0.31 mmol/mmol discriminated well between normocalciuria and hypercalciuria. Highlight: To our knowledge, this is the largest cohort of patients with hypoparathyroidism in which urinary calcium excretion has been systematically investigated under standardized conditions.