Forensic analysis of carbohydrate-deficient transferrin (CDT): implementation of a screening and confirmatory analysis concept is hampered by the lack of CDT isoform standards

The aim of the study was to test combinations of commercially available carbohydrate-deficient transferrin (CDT) assays for their usefulness as screening and confirmatory CDT analysis systems. A set of 292 serum samples from routine CDT analysis was analyzed by two assays based on anion-exchanger microcolumn CDT and non-CDT fractionation followed by a turbidimetric immunoassay (ChronAlcol.D. and %CDT TIA) and a high-performance liquid chromatography with on-line sample preparation (ClinRep CDT on-line). The CDT analysis results were divided into four groups based on the test-specific borderlines of the compared methods: NN with negative CDT results by both tests, PN with positive screening but negative confirmation results, NP with negative screening and positive confirmation results, and PP with positive results by both tests. Regardless of the test combination and whether applying the lower or upper limits of the borderlines, approximately one-third of contradictory (positive screening and negative confirmation or vice versa corresponding to groups PN and NP) were obtained. This was not due to analytical outliers (only 6 of 292 serum samples). Indeed, parametric and non-parametric ANOVA analysis pointed to different calibrations and/or recoveries of the three CDT assays. Our data give again evidence for the urgent need of an international CDT isoform standard material. At this time, we cannot recommend a combination of the three tests for screening and confirmatory analysis in forensic CDT testing. (C) 2004 Elsevier Ireland Ltd. All rights reserved.