Determinants of hypercalciuria and renal calcifications in chronic hypoparathyroidism: a cross-sectional study.

Hypercalciuria, impaired kidney function and renal calcifications are common in chronic hypoparathyroidism (HypoPT). We aimed to study associations between indices of known importance to the kidney in HypoPT by hypothesizing adverse effects of hypercalciuria on renal outcomes.Cross-sectional design. We identified all patients followed for chronic HypoPT at our department and who had been examined by a 24-hour urine collection for measurement of renal calcium excretion (24h U-Ca). By chart review, we identified additional biochemistry measured in close connection with the collection of urine, as well as demographic, treatments, and anthropometrics.The 166 included patients (79.5% females) had a high prevalence of hypercalciuria (65.7%). In multiple adjusted analyses, hypercalciuria was in an independent manner inversely associated with (residual) levels of plasma PTH and positively associated with levels of 1,25-dihydroxyvitamin D and ionized calcium as well as 24h U-phosphate, gender, and etiologyethology (surgical vs. non-surgical). Overall, this model explained 54% (p<0.001) of the variation in the presence of hypercalciuria. Chronic kidney disease stage three or above was present in 18.3% of the patients, and 42.6% of the 54 patients examined by renal imaging had renal calcifications. However, neither renal function nor renal calcifications were associated with 24h U-Ca.Hypercalciuria, impaired renal function and renal calcifications are common in hypoparathyroidism. Hypercalciuria is to a large extent explained by indices of known physiological importance to 24h U-Ca. However, in the present study, a high renal calcium excretion did not explain renal impairment or kidney calcifications.

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Authors: Lukas Ochsner Ridder, Torben Harsløf, Tanja Sikjaer, Line Underbjerg, Lars Rejnmark