Diagnosis of Primary Aldosteronism: Comparison of Post-captopril Active Renin Concentration and Plasma Renin Activity

Background: A common pharmacologic test for the diagnosis of primary aldosteronism (PA) is the administration of captopril to determine whether an abnormal plasma aldosterone concentration (PAC) to plasma renin activity (PRA) ratio(ARR) persists, although active renin concentration (ARC) may offer advantages with regard to processing and standardization.

Methods: A prospective, head-to-head study was conducted between Feb 2008 and Dec 2008. One hundred and fourteen patients enrolled and received captopril to aid in the diagnosis of PA in the TAIPAI intervention.

Results: Fifty-one patients were diagnosed with PA. Post-captopril ARC was significantly correlated with PRA. The area under the receiver operating characteristic curve of the post-captopril ARR was not different in PRA vs ARC measurements. When post-captopril ARC-based ARR (ARR(ARC))>35.5 as the cut-off value, we obtained sensitivity of 75.0% and specificity of 86.4% to differentiate PA from essential hypertension.

Conclusions: The correlation of individual PRA and ARC after administration of captopril was excellent; especially at the lower PRA levels. Post-captopril ARR(ARC) values used to diagnose PA are not different from post-captopril PRA-based (ARR(PRA)) values in patients without kidney, liver and heart failures. Primary aldosteronism can be diagnosed with a post-captopril cut-off value of ARR(ARC)>35.5 pmol/ng.