Re-assessment of the cut-off levels of Carbohydrate Deficient Transferrin (CDT) for automated immunoassay and multi-capillary electrophoresis for application in a forensic context

Background: The determination of Carbohydrate Deficient Transferrin (CDT) in a forensic context should be based on the use of a screening technique followed, for the "positive samples", by a confirmatory technique. The aim of this study was to compare the two most used automated screening methods for CDT analysis, immuno-nephelometric assay (INA) and multi-capillary electrophoresis (mCE), with a validated HPLC procedure, used as confirmation test, in order to re-evaluate the cut-off concentrations of the screening methods. Methods: 195 serum samples underwent CDT analysis by using the N Latex CDT direct immuno-nephelometric assay, the multicapillary system Capillarys™ and an anion exchange HPLC method with UV-visible detection at 460. nm developed and validated at our laboratories. Statistical analyses were performed by using Bland-Altman plots and ROC curves. Results and discussion: The 95% limits of agreement were ± 0.94% when comparing INA and HPLC and ± 0.60% when comparing mCE and HPLC. The ROC analysis of both INA and mCE, using HPLC as the reference method, showed that no false negative results were found when the cut-off was fixed to 1.2% for mCE and to 2.3% for INA. Conclusions: The study showed a good agreement among CDT determinations carried out either with mCE or INA or HPLC. However, the usual cut-offs of both mCE (1.3%) and INA (2.5%) should be lowered to minimize false negatives at the screening analysis.