**8.3 Strengths and limitations**

Iohexol is probably the easiest way to measure GFR. It can be used in all patients (except in patient with true allergy to contrast product). Its measurement by HPLC is probably one of the most precise compared to other cold method (inulin and iothalamate). Iohexol is the less expensive marker and the cost of HPLC is also low. More important, it must be underlined that an external quality control does exist for iohexol measurement (Equalis, Sweden). From unpublished data, it can be concluded that the inter-laboratory CV for iohexol measurement is very low (less than 5%). Such results don't exist for iothalamate and inulin, and, at least for inulin, we think that such good inter-laboratory results would not be reached (personal data). The limitations of iohexol are the lack of strong physiological data (notably regarding the tubular handling of the marker) and the relatively few studies having compared iohexol with inulin. More studies have actually compared iohexol with other GFR markers.
