Reevaluation of urinary calcium excretion as a criterion for surgery in primary hyperparathyroidism: a study on nephrolithiasis risk

The guideline for primary hyperparathyroidism (PHPT) recommends surgery for female patients with 24-hour urinary calcium levels >250 mg/day and male patients >300 mg/day, due to their risk for nephrolithiasis. The purpose of this study is to validate this criterion. We analyzed data from 595 patients undergoing surgery for PHPT. We investigated whether high urinary calcium excretion is associated with nephrolithiasis in PHPT patients, along with the presence of other factors. Nephrolithiasis was present in 224 patients and absent in 371. The 24-hour urinary calcium levels did not differ significantly between patients with nephrolithiasis and those without nephrolithiasis (p = 0.29). The sensitivity and specificity of the guideline thresholds were 54.9% and 53.8% for female patients and 37.8% and 51.5% for male patients. Receiver operating characteristic curve-derived cutoff values were similar to guideline values, but the areas under the curve were approximately 0.5, indicating poor discriminatory ability. Univariable analysis identified male sex, younger age, high serum creatinine, and elevated 24-hour urinary phosphorus, and creatinine levels were linked to nephrolithiasis (p < 0.001, p < 0.001, p < 0.001, p < 0.001 and p < 0.001, respectively). Multivariable analysis revealed that male sex and younger age were associated with nephrolithiasis (p = 0.034 and p < 0.001, respectively). Surgery reduced urinary calcium and phosphorus in both groups, with patients with nephrolithiasis showing higher post-surgery urinary creatinine. In PHPT, the risk of nephrolithiasis cannot be assessed by measuring the urinary calcium excretion level alone, and it should therefore be evaluated by considering multiple lithogenic factors.