Validity of the captopril test for identifying correctable unilateral renovascular hypertension

In order to validate the captopril test for identification of patients with renovascular hypertension (RVH), we performed the test with 118 patients suspected of suffering from RVH who were receiving antihypertensive medication. On the basis of 44 patients with proven RVH and 74 patients with primary hypertension (PH), the sensitivity, specificity and posterior probability for the captopril test were calculated separately for patients undergoing and not undergoing diuretic therapy. An absolute rise in plasma renin activity (PRA) and a relative rise in PRA served as discriminating indicators. The absolute increase of PRA after captopril administration in the absence of long-term therapy with diuretics yielded the best posterior probability in the one-dimensional model, with a sensitivity of 89% and a specificity of 97%. Linking of the variables "absolute" and "relative rise of PRA" reduced the misclassification rate to 5%. This validation allows an accurate distinction between RVH and PH on the basis of the captopril test even when antihypertensive therapy is not suspended (except for ACE inhibitors and diuretics).