Glomerular filtration rate: a comparison between Cr-EDTA clearance and a single sample technique with a non-ionic contrast agent.

An algorithm for the calculation of the glomerular filtration rate (GFR) from a single-point determination of the serum concentration of the non-ionic contrast medium iohexol has been evaluated. The algorithm is based upon the assumption that the distribution volumes of iohexol and 51Cr-EDTA are similar. It includes correction factors for non-immediate mixing and irregular extracellular distribution during the elimination phase. The calculated GFR from single-point determinations of iohexol obtained at 180, 200, 220 and 240 min after injection of 5 mL of this compound (300 g iodine/L) were compared with the results from simultaneously performed 51Cr-EDTA clearance in 98 patients. The single-point iohexol clearance values calculated from the different sampling times showed a coefficient of correlation of more than 0.95 to 51Cr-EDTA clearance.