GFR measured by iohexol: the best choice from a laboratory perspective
To rigorously assess glomerular filtration rate (GFR), it is necessary to measure renal inulin clearance. This procedure is, however, cumbersome and difficult for routine clinical and can be replaced by determining the clearance of radiolabeled compounds or contrast media that fulfil the criteria for ideal filtration marker. The non-ionic contrast agent iohexol is the most widely used and studied alternative marker for GFR measurement. Plasma clearance is determined after intravenous administration of 5–10 mL of the pharmacological preparation and subsequent multiple sample drawings, according to different schedules or even with single specimen protocols. Iohexol in biological matrices is readily determinable, with sufficient sensitivity and specificity by means of the most commonly used analytical technologies: sample preparation is fast and the compound is quite stable in biological samples, either at room temperature or, for longer-term storage, at −20 or −80 °C. The participation of the laboratory in the international proficiency test acted by Equalis AB, Sweden, is highly recommended to ensure reliable results and enable interlaboratory comparison of the data. To improve patient comfort and reduce pre-analytical steps, simplified procedures for GFR measurement requiring only 10 µL of whole blood [dried blood spot testing (DBS)] are valid alternatives to plasma clearance and require minimal analytical method modification for analysis. Iohexol administration for GFR measurement is a safe procedure, even in repeated investigations in the same subject, with no occurrence of major or sever adverse events. Plasma clearance of iohexol for renal function determination has a number of advantages: it is a cheap, very simple approach that is not technically demanding and is easy to implement in every centre. The choice of iohexol offers both laboratorians and clinicians the opportunity to easily select and adjust to the most appropriate approach for reliable and accurate GFR measurement.