Sakhaee K, Maalouf N, Poindexter J, Adams-Huet B, Moe O

BACKGROUND Calcium nephrolithiasis is associated with an increased risk of osteoporosis and fracture. Hypercalciuria has been assumed to be pathogenic for bone loss in kidney stone formers (KSF), although this association was shown in small cross-sectional studies. We explored the association of urine calcium (UCaV) with bone mineral density (BMD) in KSF.

METHODS We retrospectively studied BMD in KSF. Excluded were subjects with hypercalcemia, chronic bowel disease, primary hyperparathyroidism, distal renal tubular acidosis or endogenous creatinine clearance<40 ml/min. We included 250 males and 182 females, subdivided into premenopausal, estrogen-treated postmenopausal (E+) (N=145) and non-estrogen-treated postmenopausal (E-) (N=37). We assessed the association between lumbar spine (LS) and femoral neck (FN) BMD and 24-hour UCaV (under random and restricted diet, and fasting state) using univariable and multivariable models adjusting for BMI, urine sodium and sulfate.

RESULTS In multivariable analysis, no significant association found between UCaV under random and restricted diet, or fasting conditions (FS), and FN or LS BMD in men and E+ women. In E- women, LS BMD was inversely correlated with UCaV with restricted diet (r=-0.38, P=0.04 and adjusted r=-0.45, P=0.02) and in FS (r=-0.42, P=0.05).

CONCLUSIONS Unlike previous small cross-sectional studies, we found no significant relationship between UCaV and BMD in a large group of calcium KSF. However, a significant inverse relationship was found in E- KSF only. This study suggests that mechanism(s) other than hypercalciuria explain lower BMD and higher fracture risk in patients with KSF, and highlights the role of estrogen on integrity of the bone.

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