Primary hyperparathyroidism, hypercalciuria, and bone recovery after parathyroidectomy

Background. In primary hyperparathyroidism, successful parathyroidectomy leads to improved bone mineral density in the majority of cases. Our aim was to further explore the relationship between hypercalciuria, kidney function, and bone recovery after parathyroidectomy. Methods. Bone mineral density, estimated glomerular filtration rate, and 24-hour urinary calcium were analyzed before and one year after parathyroidectomy in a cohort of 150 primary hyperparathyroidism patients (119 women; median age 60 [range 30-80] years) taking part in a clinical trial. The patients were randomized to 1-year daily treatment with either cholecalciferol 1,600 IU and calcium carbonate 1,000 mg or calcium carbonate alone. Results. Baseline 24-hour urinary calcium correlated directly with s-calcium, parathyroid hormone, 25-OH-D, the bone markers beta C-terminal telopeptide of type 1 collagen and procollagen type 1 amino-terminal propeptide, and estimated glomerular filtration rate (r = 0.19-0.30; P < .05) and inversely with age (r = -0.25; P = .004); 24-hour urinary calcium decreased and bone mineral density in lumbar spine and hip increased similarly in the 2 groups. Baseline 24-hour urinary calcium in the highest quartile (> 10 mmol/d) was associated with greater increases in all locations. In a multivariable model adjusting for age, sex, smoking, diabetes, body mass index, estimated glomerular filtration rate, baseline bone mineral density, and vitamin D group, the increase in total hip bone mineral density remained independently associated with baseline 24-hour urinary calcium in the highest quartile (>10 mmol/d) and with plasma parathyroid hormone. Patients with persistent increases in 24-hour urinary calcium at follow-up (14%) had similar bone mineral density improvement. Conclusion. Overall, 24-hour urinary calcium > 10 mmol/d was an independent determinant of improvement in bone mineral density and should be taken into account when considering parathyroidectomy.