Analysis of screening and confirmatory tests in the diagnosis of primary aldosteronism: need for a standardized protocol

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Abstract
The upright serum aldosterone/upright plasma renin activity ratio (ARR) has been recommended as a screening tool for the diagnosis of primary aldosteronism. We reviewed the data collected from hypertensive patients in order to define retrospectively the cut-off values and evaluate the reliability of the ARR and of the saline infusion test in the diagnosis of primary aldosteronism. In 157 patients referred to our unit with a suspicion of primary aldosteronism, 61 of whom had confirmed primary aldosteronism [26 aldosterone-producing adenoma (APA); 35 idiopathic hyperaldosteronism], the supine and upright ARR, and the ARR after the administration of captopril and losartan were calculated, and the results of the saline infusion test were analysed. Choosing 40 as the cut-off value, the upright ARR had 100% sensitivity and 84.4% specificity. The post-captopril and post-losartan ARR were slightly more specific, but at the cost of a lower sensitivity. A cut-off value of 7 ng/dl for serum aldosterone at the end of the saline infusion in patients with an upright ARR of 40, gave 100% specificity and a positive predictive value. Furthermore, APA patients showed increased mean levels of aldosterone/cortisol ratio after the saline infusion test. Our data reinforce the superiority of a standardized upright ARR as a screening test in the diagnosis of primary aldosteronism, identifying 40 as an ideal cut-off value. Saline infusion represents a useful test to confirm such a diagnosis, with a serum aldosterone level of 7 ng/dl as a satisfactory cut-off value. Some more information is obtained when the aldosterone/cortisol ratio is considered.