Experiences in C.D.T. testing

The value of carbohydrate deficient transferrin (CDT) as the most direct and most accurate indicator of alcohol abuse has been amply demonstrated in the scientific literature. The CDT assay used by GIB Laboratories to assess serum samples for significant levels of alcohol abuse was validated using 184 clinically defined positive and 203 clinically defined negative specimens. Using a defined cutoff of significance and a special testing algorithm, GIB Laboratories has determined, in this study, that the sensitivity of the commercial CDT enzyme immunoassay (CDT EIA) is 88 percent, the specificity is greater than 99 percent, and the intra- and inter-run reproducibility is less than seven percent, about three times more precise than most confirmatory tests for CDT. Given the very low expected frequency of true physiological causes of non-specificity (less than one percent), the excellent specificity of the assay (in GIB Laboratories' experience), and the technical problems, time delays, and costs associated with all "confirmatory" technologies, it cannot be recommended that CDT confirmatory testing be performed, unless an individual laboratory experiences unacceptable specificity in its screening tests. It would appear that, performing CDT "confirmatory" testing when the specificity of the screening test is as high as this study has found it to be, can result in three probabilities: 1) an increase in the number of false negative results; 2) few corrections in the very small number of false positive results; and 3) in greater cost and delay for the laboratory's clients.