CAPTOPRIL RENOSCINTIGRAPHY WITH TC-99M DTPA IN PATIENTS WITH SUSPECTED RENOVASCULAR HYPERTENSION PROSPECTIVE AND RETROSPECTIVE EVALUATION

Sensitivity and specificity of captopril renoscintigraphy (CRS) with T c-99m DTPA has been analyzed in 41 cases, 16 with renovascular hyperte nsion (RVH) and 25 with non-RVH. The sensitivity and specificity of th e baseline study were 63% (10/16) and 63% (12/19), respectively, based on the split renal function study in which the lower limit of normal was assumed to be 42% of the total renal uptake. Captopril renoscintig raphy yielded 67% (12/18) sensitivity and 76% (19/25) specificity. The low specificity of CRS was due to the application of a prospective cr iterion of the captopril-induced reduction rate (CRR) of less than -20 %, which was calculated from the renal uptake before and after captopr il. When criteria of CRR less than -25% were used, the specificity of CRS was improved to 96%, but the sensitivity declined to 61%. Changes in the configuration of the renogram induced by captopril also had hig h specificity but low sensitivity. Renovascular hypertension was most likely when criteria for both CRR and the renogram were fulfilled. The se criteria often were diagnostic in patients with bilateral renal art ery stenosis that showed variable scintigraphic responses to captopril challenge. Captopril renoscintigraphy is a very specific means to eva luate RVH, but may have limitations in certain clinical situations suc h as poorly preserved function of the affected kidney, prior long-term administration of captopril, prior surgical manipulation of stenotic renal artery, and chronic renal parenchymal damage.