A rapid assay for icodextrin determination in plasma and dialysate.

Icodextrin is a glucose polymer osmotic agent used to achieve sustained ultrafiltration during long peritoneal dialysis dwells. Previous assays for icodextrin in plasma and dialysate samples involved laborious methods, such as gel permeation chromatography with post-column derivatization of the eluted glucose polymers. We developed and validated a simple and more rapid assay for icodextrin using amyloglucosidase to hydrolyze all glucose polymers to glucose. Glucose was determined pre- and post-hydrolysis using a glucose hexokinase assay, and icodextrin concentration was calculated as the difference between glucose levels before and after hydrolysis. The complete hydrolysis of icodextrin to glucose was confirmed using anion exchange chromatography. Recovery studies using icodextrin powder added to plasma or dialysate showed 100% +/- 15% recovery for plasma concentrations from 10 mg/dL to 800 mg/dL and for dialysate concentrations from 50 mg/dL to 800 mg/dL. The percent relative standard deviation (%RSD) based on multiple replicates was within 6%, except at plasma icodextrin concentrations of 10 mg/dL and below. This simple and reliable assay has been used routinely in our laboratory to analyze thousands of plasma and dialysate samples from patients using Extraneal peritoneal dialysis solution (Baxter Healthcare Corporation, Deerfield, IL, U.S.A.).