The Estimate of Glomerular Filtration Rate during Urography: Acceptability of a Nonionic Contrast Medium as a Marker of Renal Function

RATIONALE AND OBJECTIVES.An estimate of glomerular filtration rate (GFR) may be obtained at the same time as urography by measuring the plasma clearance of the radiographic contrast medium using an x-ray fluorescence technique. It must be established whether the function measured or one modified by an effect of the contrast medium itself represents a true value. METHODS.Technetium 99m-DTPA (Tc-DTPA) plasma clearance was measured in 21 patients using a single-injection technique, before, during, and after an intravenous injection of 50 mL of 350 mg I/mL iohexol. Iohexol clearance also was determined using an alternative single-injection, two-sample technique. RESULTS.The mean Tc-DTPA clearances before, during, and after contrast were 71.2, 71.5, and 70.7 mL/minute, respectively. The within-patient standard deviation in clearance values was 3.84 mL/minute. One factor repeat measures analysis of variance indicated no significant difference between the three measurements (F ratio = 0.24). Contrast and Tc- DTPA clearances performed simultaneously agreed closely (r = .976; CIDTPA = 1.020CICon – 1-35). CONCLUSION.The authors conclude that no change in function is observed during or 48 hours after contrast injection. Imaging doses of iohexol can be used for GFR measurement during urography.