Determination of glomerular filtration rate using iohexol clearance and capillary sampling.

Glomerular filtration rate can be conveniently quantified by monitoring the plasma clearance of iohexol. In this study we have evaluated the possibility of further simplifying the investigation by using capillary sampling. Eight women and two men were given a single injection of iohexol (5 ml Omnipaque). Three to 4 h after the injection plasma and capillary samples were taken. Iohexol concentrations in whole blood and in plasma were measured by high-performance liquid chromatography after precipitation with perchloric acid. Iohexol in blood was quantitatively distributed to the plasma compartment. Plasma concentrations of iohexol calculated from the capillary blood concentration and erythrocyte volume fraction were in good agreement with actual plasma concentrations (r = 0.98). The imprecision of iohexol determination in capillary samples was 3.5% (CV) and clearance measurements using venous and capillary sampling also agreed well.