Endocrine Abstracts

Objective: One of the ways to predict nephrolithiasis, which is one of the surgical indications in patients with asymptomatic primary hyperparathyroidism, is to detect hypercalciuria. A calcium excretion of >400 mg/day in 24-hour urine, >4 mg/kg/day calcium excretion in 24-hour urine or a fractionated calcium excretion (FECa) >0.010 guide us in the detection of hypercalciuria and therefore nephrolithiasis. The aim of our study is which of these three tests is more useful in predicting nephrolithiasis and therefore in determining the indication for surgery in asymptomatic patients.

Materials and Methods: Biochemical examinations and imaging methods records of patients diagnosed with primary hyperparathyroidism (n=271) at Dokuz Eylul University Hospital Endocrinology and Metabolic Diseases Department between 2016-2022 were retrospectively analyzed and the predictive power of the aforementioned hypercalciuria screening tests for nephrolithiasis was compared.

Results: Median age at diagnosis was 56, adjusted calcium 10.9 mg/dl, estimated glomerular filtration rate 95 ml/min, 25-OH (hydroxy) vitamin D 17 ng/ml, phosphorus 2.8 mg/dl, parathormone 156 pg/ml, adenoma size (maximum) 12 mm and fractionated calcium excretion was 0.016 of the patient included in our study. There was no significant difference in adjusted calcium, phosphate, parathormone and 25-OH vitamin D levels between patients with and without nephrolithiasis.A significant difference was found in terms of median age at diagnosis, urinary calcium and fractionated calcium excretion. There was a significant difference between categorical variables in terms of urinary calcium >400 mg/day and urinary calcium >4 mg/kg/day. According to univariate analysis results, phosphorus (P=0.017), 24-hour urinary calcium (P=<0.05), urinary calcium >400 mg/day (P=0.002), urinary calcium >4 mg/kg/day (P=0.003) and fractionated calcium excretion (P=0.005) were significant in terms of nephrolithiasis. According to the results of univariate analysis, we determined that male gender increased the probability of nephrolithiasis by 2 times. It was determined that low phosphorus increased the probability of nephrolithiasis 1.8 times, urinary calcium excretion >400 mg/day 3.2 times, urinary calcium excretion >4 mg/kg/day 2.3 times and fractionated calcium excretion 16.3 times. According to the results of multivariate analysis, we found that fractionated calcium excretion (P=0.007) was significant in terms of nephrolithiasis and it was found that it increased the probability of nephrolithiasis 20.7 times. There were no significant findings in terms of gender, age at diagnosis, adjusted calcium, phosphorus, estimated glomerular filtration rate and parathormone.

Conclusions: As a result of our study, all three hypercalciuria tests were found to be significant in terms of predicting nephrolithiasis. However, the most valuable of these tests, which is also the aim of our study, was found to be fractionated calcium excretion.

Keywords: Primary Hyperparathyroidism, Hypercalciuria, Nephrolithiasis