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

Background: The upright serum aldosterone/upright plasma renin activity ratio (ARR) has been recommended as a screening tool for the diagnosis of primary aldosteronism.

Objective: 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.

Patients: 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.

Results: 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.

Conclusion: 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.