Routine determination of GFR in renal transplant recipients by HPLC quantification of plasma iohexol concentrations and comparison with estimated GFR

Abstract

Estimated glomerular filtration rate (eGFR) methods are not sufficiently reliable in renal transplant recipients (RTR) and should be replaced by iohexol plasma clearance measurement. However, this method has poor availability in health centers. The aim of our study was to develop a high-performance liquid chromatography (HPLC) method for plasma iohexol measurement in routine practice and to evaluate its plasma clearance as a reference of GFR. We developed an HPLC method using UV detection. We evaluated sample storage conditions to provide recommendations for routine practice. Then, we compared GFRbased on plasma iohexol clearance (GFR-iohexol) to eGFR using modification of diet in renal disease, Cockcroft and Gault, and CDK-EPIequations in 40 RTR. The method was validated over a concentration range of 15-300 μg/l. Excellent linearity (r > 0.998), inter- and intraday precision (CV < 3.3%), and accuracy (>96.8%) were complied with ICH guidelines. We also demonstrated excellent samples stability (9 days). Although eGFR methods are not references in RTR, we found a correct concordance between eGFR and GFR-iohexol in our population. To conclude, our method is simple, rapid, accurate, and reliable for routine clinical and research use especially in RTR.

Figure 1

Chromatogram showing peaks of iohexol isomers and peak corresponding to internal standard (PAH).

Figure 2

Calibration curve of iohexol measured by HPLC method.

Figure 3

[Color online.] Bland and Altman plots representing different storage and time conditions of plasma samples (i.e., quality controls: 50‐100‐150 μg/ml). Blue, green, black, red points and lines represent the median and the first and third quartiles for the following storage conditions: freeze‐thaw cycles (blue), storage at –20°C (green), storage at 4°C (black), storage at room temperature (red), respectively. The reference was the measure of iohexol concentrations on fresh plasma.

Figure 4

Bland and Altman plots representing different GFR evaluation methods: (A) MDRD equation vs. iohexol clearance; (B) Cockcroft and Gault equation vs. iohexol clearance; (C) CKD‐EPI equation vs. iohexol clearance. Gray lines represent the median and the first and third quartile.