Suitability of a simplified technique based on iohexol for decentralized measurement of glomerular filtration rate

The aim of the study was to assess a simplified method for measuring glomerular filtration rate (GFR) using iohexol that could form the basis of a decentralized service for measuring GFR by sample transportation.

Non-fasting GFR was measured with Cr-51-EDTA and iohexol injected simultaneously into opposite arms (n = 110). Cubital venous blood samples, obtained bilaterally 20, 40, 60, 120, 180 and 240 min after injection, were assayed for marker injected contralaterally, Cr-51-EDTA by well-counting and iohexol by X-ray fluorescence. Following biexponential analysis of the clearance curves, GFR was measured from all six samples and also from the last three samples and scaled to body surface area (BSA). GFR scaled to extracellular fluid volume (GFR/ECV) was calculated from six samples as the mean transit time of marker through its distribution volume and from three samples as the clearance half-time.

Cr-51-EDTA correlated closely with iohexol for measuring GFR/BSA (r = 0.97 for three samples, 0.94 for six). The two markers agreed more closely with each other in the measurement of GFR/BSA compared with GFR/ECV. GFR/BSA values showed better agreement with corresponding GFR/ECV values when they were measured with Cr-51-EDTA compared with iohexol. Six samples offered no significant advantage compared with three.

Iohexol is less accurate than Cr-51-EDTA and scaling to BSA is more robust than scaling to ECV. Nevertheless, iohexol has potential to measure GFR by sample transportation, without having to measure injected dose. This would allow accurate measurement of GFR in a primary care setting.