Parenchymal mean transit time analysis of Tc-99m-DTPA captopril renography

Proposed renal hemodynamic mechanisms of captopril suggest that quantitatio n of renographic retention parameters should help identify patients suspect ed of having renovascular disease. The parenchymal mean transit time (MTT) is theoretically superior to other measures of retention, but data supporti ng its superiority are few. Methods: Two groups of subjects were studied wi th diethylenetriamine pentaacetic acid (DTPA) baseline and captopril renogr aphy, one (n = 43) with demographically defined essential hypertension (gro up I) and the other (n = 60) with a high prevalence of renovascular disease (group II). Abnormal parenchymal MTT values were derived from the statisti cal confidence limits of group I data and then applied to group II subjects for comparison with angiographic results. Results: Depending on the sensit ivity 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 subjec ts, and 23% had nondiagnostic renograms. Conclusion: Parenchymal MTT analys is of DTPA captopril renography is not more ar;curate and offers no advanta ges compared with qualitative renography or with more commonly used renogra phic measures in our subjects. This may relate to the high prevalence of re nal 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 amon g patients suspected of having renovascular hypertension.