The accuracy of combining aldosterone to renin ratio and low renin level in diagnosing primary aldosteronism

Objective: To evaluate the accuracy of combing serum aldosterone to plasma rennin ratio (ARR) and low renin level in diagnosing primary aldosteronism (PA).

Methods: The ratio of serum aldosterone to plasma renin was determined in 100 patients with PA and 61 patients with primary hypertension. The optimum cut-point of ARR was determined by the Receiver Operating Characteristic (ROC). The sensitivity, specificity, positive likelihood ratio, negative likelihood ratio and Youden index of the ARR at the optimum cut-off point were calculated in a separate test. The sensitivity and specificity of combining ARR and low renin level or high aldosterone level in diagnosing PA were determined.

Results: The supine ROC area under the curve (AUC1) was 0.991. The erect ROC area under the curve (AUC2) was 0.988. The AUC1 and AUC2 had no significant difference (P = 0.879). But they were both different significantly from with the area under the reference line (0.5) (P = 0.000). The optimum cut-off point of supine ARR was 112.06, with 0.96, 0.95, 0.91, 19.59 and 0.04 in sensitivity, specificity, Youden index, positive likelihood ratio and negative likelihood ratio, respectively. Combining ARR and low renin level produced a sensitivity and specificity of 0.422 and 0.998, respectively, in diagnosing PA. Combining ARR and high aldosterone level produced a sensitivity and specificity of 0.854 and 0.994, respectively in diagnosing PA. The optimum cut-off point of erect ARR was 36.61, with 0.99, 0.93, 0.92, 15 and 0.01 in sensitivity, specificity, Youden index, positive likelihood ratio and negative likelihood ratio, respectively. Combining ARR and low renin level produced a sensitivity and specificity of 0.941 and 0.986, respectively, in diagnosing PA. Combining ARR and high aldosterone level produced a sensitivity and specificity of 0.604 and 0.999, respectively in diagnosing PA.

Conclusions: Erect ARR (> or = 36.61) can be used in detecting PA. Combining ARR and low renin level improves the accuracy in diagnosing PA and reduces misdiagnosis. The method is simple and available. It can be carried out in the out-patient department.