Hypercalciuria: its value as a predictive risk factor for nephrolithiasis in asymptomatic primary hyperparathyroidism?

Context: The latest guidelines of the 4th International Workshop on Asymptomatic Primary Hyperparathyroidism (aPHPT) reintroduced hypercalciuria (i.e. urinary calcium > 400 mg/day) as criterion for surgery. However, the value of hypercalciuria as a predictor of nephrolithiasis and the correct cut-off values still need to be confirmed. Objective: To evaluate the prevalence of silent kidney stones in a large series of patients with aPHPT and the sensibility, specificity and predictive value of different cut-off values of hypercalciuria in identifying patients with nephrolithiasis. Design: One hundred seventy-six consecutive patients with aPHPT were evaluated at our Institution by serum and urinary parameters and kidney ultrasound. Results: Silent nephrolithiasis was found in 38 (21.6%) patients. In the univariate and multivariate model, hypercalciuria was a predictor of nephrolithiasis using the criterion of 400 mg/24 h [(OR 2.30, (1.11–4.82) P = 0.025], 4 mg/kg/bw [OR 2.65, (1.14–6.25) P = 0.023], gender criterion [OR 2.79, (1.15–6.79) P = 0.023] and the cut-off value derived from the ROC analysis [(> 231 mg/24 h) OR 5.02 (1.68–14.97) P = 0.004]. Despite these several predictive criteria, however, hypercalciuria had a low positive predictive value (PPV), ranging from 27.4 to 32.7%. Conclusions: Hypercalciuria is a predictor of nephrolithiasis, but its PPV is low.