We performed a prospective head-to-head comparison of the accuracy of the captopril test (CAPT) and the saline infusion test (SAL) for confirming primary aldosteronism due to an aldosterone-producing adenoma (APA) in patients with different sodium intake. A total of 317 (26.9%) of the 1125 patients screened in the Primary Aldosteronism Prevalence in Italy Study underwent both CAPT and SAL. They were composed of the patients with a high aldosterone/renin ratio baseline and 1 every 4 patients without such criterion. The accuracy of post-CAPT or post-SAL plasma aldosterone values for diagnosing APA was estimated with the area under the receiver operator characteristics curves. Primary aldosteronism was found in 120 patients, of which 46 had an APA. No untoward effect occurred with either test. The area under the receiver operator characteristics curve of plasma aldosterone for both tests was higher (P<0.0001) than that under the diagonal, but the between-test difference was borderline significant (P=0.054). The optimal aldosterone cutoff value for identifying APA was 13.9 and 6.75 ng/dL for the CAPT and SAL, respectively. Even at these cutoffs, sensitivity and specificity were moderate because of overlap of values between patients with and without APA. When examined in relation to sodium intake, the accuracy of the SAL surpassed that of the CAPT in the patients with a sodium intake <or=130 mEq per day; this difference waned at a higher Na(+) intake. Thus, both the CAPT and the SAL are safe and moderately accurate for excluding APA; at a sodium intake >7.6 g per day, the SAL offers no advantage over the easier-to-perform CAPT.
