Renal fraction of cardiac output cleared of radioactive indicator in 99Tcm-DTPA gamma camera renography.

The renal images recorded during 1 to 2 1/2 min postinjection in 99Tcm-DTPA gamma camera renography were used for determination of the total cleared renal fraction (TCRF) of cardiac output with respect to the radioactive indicator. The left and right cleared renal fractions of cardiac output were determined directly, i.e., assessment of single-kidney uptake function within a few minutes postinjection was also possible. TCRF was proportional to the glomerular filtration rate (GFR) determined by the 51Cr-EDTA plasma clearance in a group of 23 subjects with GFR in the interval 15 to 130 ml/min/1.73 m2. The slope of the regression line of TCRF against GFR was in agreement with the theoretical estimate for it. GFR could be predicted from TCRF with a standard error of estimate from 4 to 15 ml/min/1.73 m2 for values of GFR in the above interval. Intra-observer variability of TCRF was unbiased and varied between 4% (normal GFR) and 9% (decreased GFR). TCRF is proposed to represent an alternative to renal clearance for evaluation of renal uptake function.