Equipment for Estimation of Contrast Clearance

A new method for determining the glomerular filtration rate was analysed prospectively. The method uses an x ray fluorescence technique to measure disappearance from the plasma of injected non-ionic iodinated contrast media. Eighty seven patients were studied. Fifty four had an intravenous dose of 100 ml iohexol (Omnipaque) and 33 had 50 ml iohexol. Clearances ofchromium-51 labelled edetic acid ("Cr-EDTA) were measured simultaneously. In the patients given 100 ml iohexol there was excellent correlation with 5"Cr-EDTA clearance (r=0-90). The correlation using 50 ml iohexol was also good (r=0-85). Correlation between creatinine clearance and clearance of5Cr-EDTA in 33 patients was less satisfactory (r=0'69). There were no adverse reactions to the contrast media. The equipment used for measuring contrast clearance was robust and simple to operate. Freezing plasma samples in 10 studies and re-examining them weekly for six weeks showed no significant variation in results; hence reproducibility was good. This new and accurate method for determining the glomerular filtration rate merits further study and might find a useful place in routine clinical practice.