Iohexol plasma clearance for measuring glomerular filtration rate in clinical practice and research: a review. Part 1 : How to measure glomerular filtration rate with iohexol?

While there is general agreement on the necessity tomeasure glomerular filtration rate (GFR) inmany clinical situations, there is
less agreement on the bestmethod to achieve this purpose. As the gold standardmethod for GFR determination, urinary (or renal)
clearance of inulin, fades into the background due to inconvenience and high cost, a diversity of filtrationmarkers and protocols
compete to replace it. In this review, we suggest that iohexol, a non-ionic contrast agent, is most suited to replace inulin as the
marker of choice for GFR determination. Iohexol comes very close to fulfilling all requirements for an ideal GFRmarker in terms of
low extra-renal excretion, low protein binding and in being neither secreted nor reabsorbed by the kidney. In addition, iohexol is
virtually non-toxic and carries a low cost. As iohexol is stable in plasma, administration and sample analysis can be separated in
both space and time, allowing access to GFR determination across different settings. An external proficiency programme operated
by Equalis AB, Sweden, exists for iohexol, facilitating interlaboratory comparison of results. Plasma clearance measurement is
the protocol of choice as it combines a reliable GFR determination with convenience for the patient. Single-sample protocols
dominate, butmultiple-sample protocolsmay bemore accurate in specific situations. In lowGFRs one ormore late samples should
be included to improve accuracy. In patients with large oedema or ascites, urinary clearance protocols should be employed. In
conclusion, plasma clearance of iohexol may well be the best candidate for a common GFR determination method.