Validation of the ultrafiltration technique for creatinine analysis by HPLC: a comparison with direct serum injection

The determination of creatinine by HPLC was performed by direct injection of serum onto the column, and after ultrafiltration of the sample, and the results were compared. A modified weak cation exchange column was used for HPLC. This eliminates the protein displacement effect and the Gibbs-Donnan effect, thus permitting a rapid direct analysis. Three of the four ultrafiltration methods gave almost identical analytical results. Regression analyses of the results from direct serum injection versus ultrafiltration showed a bias of 5% on the slope y = 1.050 . xpure serum + 1.856, which was in our view solely due to the volume displacement effect of the proteins; correction of each data point by a protein-dependent correction factor resulted in an almost perfect regression line.