The plasma aldosterone concentration:renin ratio (ARR) is widely used for the screening of primary aldosteronism, but its reproducibility is unknown. We, therefore, investigated the within-patient reproducibility of the ARR in a prospective multicenter study of consecutive hypertensive patients referred to specialized centers for hypertension in Italy. After the patients were carefully prepared from the pharmacological standpoint, the ARR was determined at baseline in 1136 patients and repeated

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... after, on average, 4 weeks in the patients who had initially an ARR Ն40 and in 1 of every 4 of those with an ARR Ͻ40. The reproducibility of the ARR was assessed with Passing and Bablok and Deming regression, coefficient of reproducibility, and Bland-Altman and Mountain plots. Within-patient ARR comparison was available in 268 patients, of whom 49 had an aldosterone-producing adenoma, on the basis of the "4-corner criteria." The ARR showed a highly significant within-patient correlation (rϭ0.69; PϽ0.0001) and reproducibility. Bland-Altman plot showed no proportional, magnitude-related, or absolute systematic error between the ARR; moreover, only 7% of the values, for example, slightly more than what could be expected by chance, fell out of the 95% CI for the between-test difference. The accuracy of each ARR for pinpointing aldosterone-producing adenoma patients was Ϸ80%. Thus, although it was performed under different conditions in a multicenter study, the ARR showed a good within-patient reproducibility. Hence, contrary to previously claimed poor reproducibility of the ARR, these data support its use for the screening of primary aldosteronism. (Hypertension. 2010;55:83-89.) Key Words: secondary hypertension Ⅲ aldosteronism Ⅲ renin assay Ⅲ aldosterone Ⅲ diagnosis R ecent compelling evidence indicates that primary aldosteronism (PA) is associated with prominent cardiovascular and renal damage, adverse metabolic consequences, and an excess rate of cardiovascular events. 1-3 In the Primary Aldosteronism Prevalence in hYpertension (PAPY) Study, PA was diagnosed in 11.2% of 1125 newly diagnosed hypertensive patients referred to hypertension centers; moreover, in 4.8% it was attributed to an aldosterone-producing adenoma (APA). 4 Therefore, it is likely that PA represents the most common form of endocrine arterial hypertension that is surgically curable in a substantial proportion of the cases. Currently the plasma aldosterone concentration (PAC):renin ratio (ARR) is the most popular screening test for identifying PA, 4,5 and although it has obvious limitations, 6 its widespread adoption can enhance the identification of PA. 7 Nonetheless, the within-patient reproducibility of this test remains unknown. 8 We report here the results of the study of within-patient comparison of the ARR that was determined at the baseline screening and repeated on average after a month. Subjects and Methods All of the patients originally recruited in the PAPY Study and 11 additional patients who were investigated with an identical protocol at the internal medicine department of the General Hospital of Legnano were included in this study. The PAPY Study protocol followed the Statement for Reporting Studies of Diagnostic Accuracy recommendations 9 and the requirements of the Declaration of Helsinki. 4 Briefly, consecutive newly diagnosed hypertensive patients, referred to specialized hypertension centers nationwide in Italy, were recruited after informed consent was obtained. 4 A previous diagnosis of a secondary form of hypertension and the Continuing medical education (CME) credit is available for this article. Go to http://cme.ahajournals.org to take the quiz.