FRI687 Clinical Relevance Of 24-hour Urine Calcium Measurement In Patients With Primary Hyperparathyroidism (PHPT)

Abstract Disclosure: A. Bhan: None. R. Simon: None. G. Jacobsen: None. A. Yaseen: None. P. Navaratnarajah: None. A. Sweidan: None. S.D. Rao: None. Introduction: PHPT is the third most common endocrine disease and the most common cause of hypercalcemia in outpatient setting, presents with mild to moderate hypercalcemia with unsuppressed or elevated serum PTH levels, and most patients are asymptomatic. A 24-hour urine Ca measurement to exclude both hypo- and hypercalciuria is used to recommend parathyroidectomy. The purpose of our study is to evaluate the clinical relevance of urine Ca measurement in evaluating patients with PHPT. Methods: A retrospective electronic medical record review was performed on all adult patients with PHPT in whom a 24-hour urine Ca was measured between 2015-2019. Patients with secondary HPT, those without a 24-hour urine Ca measurement, and patients with serum Cr >1.5 mg/dl were excluded. Results: 393 patients met inclusion criteria for subsequent analyses. For the entire cohort, mean serum Ca was 10.9 ± 0.6 mg/dl, Cr 0.9 ± 0.2 mg/dl and PTH 111± 65 pg/ml with no significant difference between groups by gender, race, or stone history. Mean urine Ca for the entire cohort was 254 ± 170 mg/day. 46% and 35% had urine Ca >250 or >300 mg/d respectively. Multiple linear regression results indicated that higher serum Ca (p=0.004), lower serum Cr (p<0.001), white race (p<0.001), and higher urine sodium (p<0.001) were all significantly predictive of higher UCa. However, the mean urine Ca did not differ between patients with and without nephrolithiasis (276 ± 182 Vs. 280 ± 247 mg/d; p=0.174). Discussion: The most recent guidelines for the management of asymptomatic PHPT recommend measurement of 24-hour urine Ca in all PHPT patients. However, the validity, sensitivity and specificity of such an approach has never been formally evaluated, considering wide variability of urine Ca excretion in the population and lack of difference in urine Ca between patients with and without nephrolithiasis. Previous guidelines discussed this issue and determined that measurement of a 24-hour urine collection is cumbersome and adds very little to patient management. Our study questions the clinical relevance of re-including 24-hour urine Ca in the latest guidelines. Conclusions: Our study suggests that measurement of 24-hour urine Ca in the routine evaluation of patients with PHPT is unhelpful. Presentation: Friday, June 16, 2023