Carbohydrate-Deficient Transferrin Results and Transferrin Variants To the Editor:

(CDT)1 is a biomarker of growing importance in the assessment of al-cohol abuse after conviction for drunk driving. CDT is a more spe-cific indicator for alcohol than tradi-tional liver function tests and is used for identification and follow-up of chronic high alcohol consumption (1). Various methods have been in-troduced forassayingCDTinserum, including isoelectric focusing, ion-exchange chromatography, HPLC, capillary zone electrophoresis (CZE), and latex enhanced immunoneph-elometry (1, 2). Measuring the CDT percent-age (%CDT) in a forensic context demands CZE orHPLCmethodol-ogy, because it provides high-resolution separation of serum transferrin (Tf) isoforms and al-lows the detection of genetic vari-ants and glycosylation disorders. In some cases, the interpretation of CDT results is hampered by the presence ofmutant Tf (3). In addi-tion to wild-type Tf (C), D variants (cathodal to C) and B variants (an-odal to C) have been described (1). The allele frequencies of the Tf subtypes vary among populations of different ethnicities (4). Exact measurement of D variants of CDT is difficult, however, because di- and trisialylated Tf may coelute with the tetrasialylated D peak in HPLC or comigrate in CZE. Algorithms have been proposed to correct for the presence of mutant Tf in capillary electropherograms (4, 5). Immunonephelometric tests in which highly specific monoclo-nal antibodies recognize the Tf gly-cosylation sites have been intro-duced. The N Latex CDT assay (Siemens) uses a monoclonal anti-body that recognizes Tf glycoforms lacking 1 or 2 complete N-glycans (i.e., disialo-, monosialo-, and asialo-Tf) (2). In addition, total Tf is measured. There is limited evi-dence for the effect ofmutant Tf on CDT test results, mainly because of the small number of participants who were enrolled in the evalua-tion study (2). Because Tf variants are common findings (particularly in non-Caucasian populations) (3, 4), knowledge of the perfor-mance of immunonephelometric tests in the presence of Tf mutants is of practical importance. In the present study, we compared the ef-fect of Tf variants on CZE and nephelometric CDT testing. The study was approved by the Ethic