Parenchymal mean transit time analysis of 99mTc-DTPA captopril renography

Proposed renal hemodynamic mechanisms of captopril suggest that quantitation of renographic retention parameters should help identify patients suspected of having renovascular disease. The parenchymal mean transit time (MTT) is theoretically superior to other measures of retention, but data supporting its superiority are few.

Two groups of subjects were studied with diethylenetriamine pentaacetic acid (DTPA) baseline and captopril renography, one (n = 43) with demographically defined essential hypertension (group I) and the other (n = 60) with a high prevalence of renovascular disease (group II). Abnormal parenchymal MTT values were derived from the statistical confidence limits of group I data and then applied to group II subjects for comparison with angiographic results.

Depending on the sensitivity of the threshold chosen, specificity varied, but the overall accuracy of baseline parenchymal MTT for renovascular hypertension detection ranged from 54% to 58%. Change in parenchymal MTT (post-captopril - pre-captopril) accuracy was 55%-61% and was not significantly different. Neither method improved on previously reported quantitative or qualitative criteria. Group II subjects had significantly worse renal function than did group I subjects, and 23% had nondiagnostic renograms.

Parenchymal MTT analysis of DTPA captopril renography is not more accurate and offers no advantages compared with qualitative renography or with more commonly used renographic measures in our subjects. This may relate to the high prevalence of renal dysfunction in our population. In subjects with renal dysfunction, the low sensitivity and the trend toward low specificity of parenchymal MTT do not support its routine use for the evaluation of renovascular disease among patients suspected of having renovascular hypertension.