632 SENSITIVITY, SPECIFICITY AND REPRODUCIBILITY OF THE ALDOSTERONE-TO-RENIN-RATIO AS A SCREENING TEST FOR PRIMARY ALDOSTERONISM

Abstract

Background: The aldosterone-to-renin ratio (ARR) is a widely used screening test for primary aldosteronism (PA). A commonly adopted cut-off value is 91 pmol/mU. However, its sensitivity, specificity, and reproducibility have not been studied extensively. Aim: To characterize the main test characteristics of the ARR. Design and methods: In 179 patients with persistent hypertension despite the use of at least 2 antihypertensive drugs plasma renin and aldosterone were assessed twice with an interval of 2 to 4 weeks. All patients underwent an intravenous salt loading test. Patients with a post-test plasma aldosterone exceeding 235 pmol/L were considered to have PA. Aldosterone and renin measurements were repeated after 4 weeks on standardized treatment with a calcium channel blocker and/or alphablocker. Sensitivity and specificity were calculated under both conditions. Reproducibility was evaluated by Bland-Altman analysis of ln-transformed ARR levels at the first (ARR1) and second (ARR2) measurement. The 95 % limits of agreement were expressed as ARR1/ARR2 ratios. Results: The prevalence of PA was 15.1 %. The median ARR was 34.4 (interquartile range 16.1-72.3) in PA patients versus 7.1 (IQR 2.2-17.5) in essential hypertensives (p<0.001). Under random medication the ARR had 19.2 % sensitivity and 98.6 % specificity. On standardized treatment the ARR rose from 9.6 (2.6-24.9) to 21.1 (10.8-52.6) (p<0.001). Sensitivity improved to 50 % with a specificity of 92.6 %. Ninety-five percent of ARR1/ARR2 ratios were between 0.22 and 4.21. Conclusion: ARR sensitivity for PA is low, even under ARR-neutral medication. Reproducibility is poor, stressing the need for alternative screening tests.