Abstract P432: Screening for Primary Aldosteronism: Effect of Test and Cutoff Level on Positivity Rate

Abstract

Background: The 2016 guidelines of the Endocrine Society proposed a screening test for primary aldosteronism (PA) based on an aldosterone renin ratio (ARR) ≥30. However, a plasma renin activity (PRA) suppressed to <1 ng/mL/h may indicate PA status better than the ARR. Methods: We conducted a retrospective analysis to compare the effectiveness of various screening tests for PA in a cohort of 94,829 consecutive patients who underwent ARR testing at Quest Diagnostics. The tests that were compared include ARR ≥20, ARR ≥30, PRA <1 ng/mL/h, and PRA <0.5 ng/mL/h. This comparison was made because the ARR tests may not be highly sensitive, while the PRA tests may not be highly specific. We also analyzed differences in test volume and positivity rate by region, race, ethnicity, and the time of day when the test was performed. Results: We observed that PRA <1 ng/mL/h identified 2.2 times as many PA cases as ARR ≥20 and 3.3 times as many cases as ARR ≥30. Likewise, PRA <0.5 ng/mL/h identified 1.3 times as many cases as ARR ≥20 and 1.9 times as many cases as ARR ≥30 (Table). We also found that PA positivity rates using ARR ≥20, ARR ≥30, PRA <1 ng/mL/h, and PRA <0.5 ng/mL/h were higher for tests performed before noon than after noon. Additionally, positivity rates were similar across US regions, although the Midwest had lower positivity for ARR tests than PRA tests, and the West had lower positivity for PRA tests than ARR tests. The PRA-based test continued to be positive more frequently than the two ARR-based tests regardless of race; however, non-Hispanic Black patients had a higher positivity rate than Hispanic, non-Hispanic White, and Asian patients, irrespective of the test used. Conclusions: Our data show that compared to PRA <1 ng/mL/h and <0.5 ng/mL/h, the ARR screening tool set at ≥20 or ≥30 potentially misses many patients with PA. If future prospective studies confirm this finding, one of the two suppressed PRA-based tests could become the preferred screening tool for PA.