Evaluation of single sample clearance calculations in 902 patients

PURPOSE: To derive new formulae for the calculation of single sample clearance of the contrast medium iohexol and to compare the formulae to a selection of existing single sample clearance formulae derived for the calculation of 51Cr-EDTA and 99mTc-DTPA clearance. MATERIAL AND METHODS: Glomerular filtration rate (GFR) was calculated from total plasma clearance of iohexol used for urography in 902 patients. Two plasma samples were drawn in each patient. Automated x-ray fluorescence analysis equipment was used for the plasma iodine analysis. Single and multiple sample iohexol clearance values were compared. In 77 patients the multiple sample clearance values were additionally compared to a 51Cr-EDTA clearance performed simultaneously or within 14 days. RESULTS: The precision of the results calculated by the existing single sample clearance formulae and the derived iohexol single sample clearance formulae were essentially the same. The most precise of the derived formulae was that based on the Bak Christensen & Groth formula. The correlation between multiple sample clearance of iohexol and 51Cr-EDTA was high (r = 0.918). CONCLUSION: Iohexol can substitute 51Cr-EDTA for GFR measurement. A valid GFR can be calculated from a single plasma sample determination of iohexol clearance using either the existing formulae or the new formulae derived from the present study.