To analyze the biochemical alterations in plasma and the urine determinants of severe lithogenic activity in patients with idiopathic calcium nephrolithiasis.

We performed a cross-sectional study of 120 patients divided into 2 groups: group 1, 60 patients without nephrolithiasis; and group 2, 60 patients with severe and/or recurrent calcium nephrolithiasis. In all patients, a study of renal function, calcium metabolism, and bone remodeling markers, and a study of the lithogenic factors were performed in urine after fasting and in 24-hour urine samples.

We observed greater values for phosphorus in group 1 than in group 2 (P = .03). Also, we found greater values for intact parathyroid hormone (P = .01), osteocalcin (P = .000), and β-crosslaps (P = .000) in group 2 than in group 1. In the 24-hour urine samples, significant differences were found between groups 1 and 2 in calciuria (11.7 vs 17.4 mg/dL; P = .000), citraturia (50.6 vs 33.5 mg/dL; P = .002), calcium/creatinine quotient (0.14 vs 0.20; P = .001), calcium/citrate quotient (0.05 vs 0.13; P = .04), and calcium/creatinine quotient after fasting (0.09 vs 0.16; P = .000).

We consider the determinants of severe and/or recurrent calcium lithiasis to be hypercalciuria and hypocitraturia and a calcium/citrate quotient >0.06. As risk markers we can consider phosphatemia <2.9 mg/dL, phosphate/chlorine quotient >35, alkaline phosphatase >80 U/L, intact parathyroid hormone >60 pg/mL, osteocalcin >16 ng/mL, β-crosslaps >0.400 ng/mL, and β-crosslaps/osteocalcin quotient >0.028.