EVALUATION OF SINGLE-SAMPLE CLEARANCE CALCULATIONS IN 902 PATIENTS - A COMPARISON OF MULTIPLE AND SINGLE-SAMPLE TECHNIQUES

Purpose: To derive new formulae for the calculation of single sample c learance of the contrast medium iohexol and to compare the formulae to a selection of existing single sample clearance formulae derived for the calculation of Cr-51-EDTA and Tc-99m-DTPA clearance. Material and Methods: Glomerular filtration rate (GFR) was calculated from total pl asma clearance of iohexol used for urography in 902 patients. Two plas ma samples were drawn in each patient. Automated x-ray fluorescence an alysis equipment was used for the plasma iodine analysis. Single and m ultiple sample iohexol clearance values were compared. In 77 patients the multiple sample clearance values were additionally compared to a C r-51-EDTA clearance performed simultaneously or within 14 days. Result s: The precision of the results calculated by the existing single samp le clearance formulae and the derived iohexol single sample clearance formulae were essentially the same. The most precise of the derived fo rmulae was that based on the BAK CHRISTENSEN & GROTH formula. The corr elation between multiple sample clearance of iohexol and Cr-51-EDTA wa s high (r=0.918) Conclusion: Iohexol can substitute Cr-51-EDTA for GFR measurement. A valid GFR can be calculated front a single plasma samp le determination of iohexol clearance using either the existing formul ae or the new formulae derived from the present study.