Radioisotopic measurement of glomerular filtration rate in severe chronic renal failure

In order to determine the best method for routine measurement of glomerular filtration rate (GFR) in severe renal failure, we compared simultaneously the urinary clearances of [99mTc] diethylenetriaminepentaacetic acid (DTPA) (UD), [125I]iothalamate (UI), 24-hr creatinine clearance (UC) and plasma clearance of [99mTc]DTPA (PD), based on three plasma samples. In 60 studies in 22 patients with serum creatinine values of 2 to 8 mg/dl, UD and UI were almost identical: UD = 0.358 +/- 0.976 UI +/- 0.87 ml/min, r = 0.990. However, PD overestimated UD by a large and variable extent: PD = 11.3 +/- 0.843 UD +/- 5.5 ml/min, r = 0.694, and was inconsistent in sequential measurements in individual patients. UC also overestimated urinary isotope clearance: UC = 4.2 + 0.95 UI +/- 3.9 ml/min, r = 0.865. Sequential measurements of GFR in five patients with severe but stable renal failure (mean GFR 5.9 ml/min) showed an average standard deviation of only 0.83 ml/min. Thus both UD and UI appear to be reliable and precise measures of GFR in severe renal failure.