Renal vascular transit time and tubular transit time dispersion for Tc-99(m)-MAG3

Renal transit time usually refers to tubular transit time, as introduced by Taplin, but other measures of renal transit have been proposed. Here we examine the vascular transit time (VIT; following Rutlandi and the standard deviation of tubular transit time (SDTT, following Britton) in a group of 30 patients having baseline and ACE-inhibitor Tc-99(m)-MAG3 renography prior to arteriography. A same-day low-dose/high-dose protocol was used for renography; only the post-captopril dose was high enough to measure VTT. Pre-captoyril, the Spearman rank correlation coefficient for SDTT was rho = 0.52 (n = 53 kidneys; P< 0.0002); post-captopril, rho = 0.54 (n = 49 kidneys; P < 0.0002), For VTT, the post-captopril value was rho = 0.24 (n = 30 kidneys; N.S.). For comparison, the same statistics were calculated fur Taplin's original measure of transit time: the time from injection to maximum count rate (peak time). Precaptopril, for peak time, rho was 0.47 (n = 53 kidneys; P < 0.001); post-captopril, rho was 0.39 (n = 50 kidneys, P < 0.01). These findings confirm the diagnostic value of SDTT but not of VTT. SDTT correlated better than peak time with the arteriographic findings.