FRI138 Diagnostic Accuracy Of Plasma Renin Activity Measured By Radioimmunoassay And LC-MS/MS For The Screening Of Primary Aldosteronism

Disclosure: A. Hong: None. J. Yoon: None. J. Park: None. W. Choi: None. H. Kim: None. H. Kang: None. Background: Plasma aldosteronism (PA) is screened based on the levels of aldosterone-to-renin ratio (ARR) and/or plasma aldosterone concentration. However, false positive cases are often observed due to low levels of plasma renin activity (PRA). Here, we aimed to compare diagnostic accuracy of PRA measured by radioimmunoassay (RIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the screening of PA. Materials and Methods: We retrospectively included 67 patients in whom PRA was measured using both RIA and LC-MS/MS due to adrenal incidentaloma or suspected secondary hypertension in a tertiary referral center. Patients with ARR≥20 underwent saline infusion test (SIT) and/or captopril challenge test (CCT) for the confirmation of PA. Results: The mean PRA was 3.1±7.5 ng/mL/hr by RIA and 3.0±6.3 ng/mL/hr by LC-MS/MS (P=0.284). The mean ARR was 53.7±137.4 by RIA and 41.2±129.9 by LC-MS/MS. The correlation coefficient between RIA and LC-MS/MS was 0.992 in patients with ARR<20 (n=38) (P<0.001) and 0.595 in patients with ARR ≥20 (n=29) (P=0.001). In patients who underwent confirmative test (CCT or SIT), false-positivity rate was 77.8% (7/9) based on RIA and 66.7% (6/9) based on LC-MS/MS. Conclusion: PRA measured using LC-MS/MS showed a significant positive correlation with PRA using RIA, particularly at ARR<20. ARR calculated by both methods for PRA revealed similar false-positives. Further studies are needed to validate diagnostic accuracy between the two methods of PRA for PA screening. Presentation: Friday, June 16, 2023