Urinary Parameters as Predictors of Primary Hyperparathyroidism in Patients With Nephrolithiasis

Abstract

Serum calcium and parathyroid hormone levels are the primary means of evaluating patients for hyperparathyroidism. Whether there are differences in urinary parameters between stone formers with and those without hyperparathyroidism is controversial. In this study we identify urinary parameters that predict primary hyperparathyroidism. From 2001 to 2010 a total of 1,190 adult, noncystine stone forming patients underwent urinary metabolic stone evaluation. Of these patients 34 (3%) underwent parathyroidectomy for primary hyperparathyroidism. Urinary parameters were evaluated as predictors of primary hyperparathyroidism. The most accurate combination of serum and urinary tests and their cutoffs were determined. Stone forming patients with primary hyperparathyroidism were more likely to be women and had higher urinary calcium excretion. Hypercalciuria (aOR 4.38), supersaturation calcium oxalate greater than 10 (aOR 4.27), supersaturation calcium phosphate greater than 2 (aOR 3.64), calcium per kg greater than 4 mg/kg (aOR 8.03) and calcium-to-creatinine ratio greater than 150 mg/gm (aOR 7.07) were significant predictors of primary hyperparathyroidism in separate multivariate models after adjustment. The best accuracy was determined using serum calcium and parathyroid hormone levels with our laboratory cutoffs (AUC 0.984) with a sensitivity of 87%, specificity of 99%, positive predictive value of 79% and negative predictive value of 99.5%. No other factor(s) improved diagnostic accuracy or could replace parathyroid hormone level. Greater urinary calcium excretion predicted primary hyperparathyroidism. Serum calcium with parathyroid hormone level was the most accurate test for primary hyperparathyroidism. No other serum or urinary parameter improved diagnostic accuracy or could replace parathyroid hormone. There were no obvious cutoffs for any of the urinary parameters that reliably differentiated cases of hyperparathyroidism.