[Evaluation of the ratio of plasma aldosterone to rennin concentration measured by an automated chemiluminescent immunoassay in screening for primary aldosteronism].

Objective: To investigate the optimal cutoff of plasma aldosterone to rennin concentration ratio (ARR) determined by an automated chemiluminescent immunoassay for primary aldosteronism (PA) screening.

Methods: A total of 154 hypertensive patients and 83 healthy volunteers were recruited in the study. Blood for aldosterone and rennin were collected from patients in the supine position and from patients and healthy volunteers after 2-hour upright posture. Plasma aldosterone concentration(PAC) and plasma rennin concentration(PRC) were determined with the automated chemiluminescent immunoassay. The diagnoses of PA were made based on clinical manifestations, confirmatory tests and pathologic results. A ROC curve analysis was performed to determine the optimal ARR cutoffs for PA.

Results: Fifty-three patients were diagnosed with PA, 85 were with essential hypertension and 16 were with other types of endocrine hypertension. In hypertensive patients, the areas under the ROC curves (AUCROC) of ARR were 0.962 (95%CI 0.933-0.990, P<0.01) in the supine position and 0.980 (95%CI 0.962-0.998, P<0.01) after 2-hour upright posture, respectively. The AUCROC of ARR was higher than that of either PAC or PRC in the same position. The highest Youden's index of ARR in the upright posture was 0.85 with the cutoff value of 119.1 pmol/mU [4.3 (ng/dl)/(mU/L)] (sensitivity 94%, specificity 91%).

Conclusion: ARR in the upright position by the automated chemiluminescent immunoassay provides a high efficiency screening test for PA. The optimal cutoff of ARR is 119.1 pmol/mU.