CDTect-RIA and CDTect-EIA for determination of serum carbohydrate-deficient transferrin (CDT) by radioimmunoassay and enzyme immunoassay respectively were tested for equality and precision in four European laboratories. For correlational studies, serum samples with CDT concentrations up to 130 U/l were analysed in accordance with a uniform trial schedule. The regression of CDT values obtained by the two procedures was computed for each laboratory using the method of Passing and Bablok. Slopes and intercepts of the regression functions did not differ significantly from the values 1 or 0, as proved by the corresponding 95% confidence intervals. Precision studies were computed using analysis of variance. For CDT concentrations at the upper reference limit for men, the within-day coefficients of variation (CVs) ranged between 0.7 and 6.4% (median 5.2%) for CDTect-RIA and from 4.3 to 9.2% (median 6.2%) for CDTect-EIA. The corresponding pure between-day CVs were 5.0-18.5% (median 9.8%) and 3.5-14.5% (median 10.9%). The study demonstrates the equality of CDT values obtained by CDTect-RIA and CDTect-EIA. According to this study, the two methods can be used interchangeably without getting fluctuating CDT values, e.g. in longitudinal studies.

Background: The introduction of a new set of reagents for the determination of carbohydrate-deficient transferrin (CDT) as a marker of chronic alcohol abuse requires an independent evaluation of the analytic specificity of the test. This information is needed for correct interpretation and classification of test results. Methods: Isoelectric focusing on the PhastSystemTM followed by immunofixation, silver staining, and densitometry was used to validate the initial transferrin isoform fractionation step on anion-exchange microcolumns involved in the ChronAlcoI.D.TM assay. Results: The in vitro transferrin iron load was complete and stable. The CDT and non-CDT transferrin fractionation on anion-exchange microcolumns was reliable and reproducible (CV ≤10%). Except for quantitatively unimportant traces of trisialo-Fe2-transferrin (<5% of total CDT), only asialo-, mono-, and disialo-Fe2-transferrin were detected in the microcolumn eluates (n = 170). There was a loss of proportionally similar amounts of asialo-Fe2-transferrin (during column rinsing) and disialo-Fe2-transferrin (on the anion exchanger). Thus, the peak height ratios for disialo- and asialo-Fe2-transferrin did not change from >1 (serum) to <1 (eluates) as described for the CDTect assays. The transferrin patterns in the ChronAlcoI.D. eluates were representative of those in serum. Transferrin D variants with isoelectric points close to that of trisialo-Fe2-transferrin C1 did not cause overdetermination of CDT by the ChronAlcoI.D. test. Conclusions: The initial CDT and non-CDT fractionation step involved in determination of CDT by the ChronAlcoI.D. assay is efficient for eliminating non-CDT transferrins from serum before quantification of CDT in the final turbidimetric immunoassay. We recommend IEF for validation of other (commercial) CDT analysis methods and of odd CDT results.