Absolute or relative measurement of carbohydrate-deficient transferrin in serum? Experiences with three immunological assays.

Characterization of proteins by capillary electro-phoresis in fused-silica columns: review on serum protein analysis and application to immunoassays. Capillary Electrophoresis of serum proteins. Reproducibility, comparison with agarose gel electrophoresis and a review of the literature. Multicenter evaluation of the Paragon CZE 2000 capillary zone electrophore-sis system for serum protein electrophoresis and monoclonal component typing. Individuals who have consumed at least 50 – 80 g of alcohol per day during the previous week(s) often show an abnormal microheterogeneity of the iron-transporting glycoprotein transferrin in serum (1). After chronic exposure to alcohol, the concentrations of transferrin molecules that lack 2– 4 of the four normal terminal sialic acid residues (di-, mono-, and asialo transferrin, respectively) (1) or that lack the entire biantennary carbohydrate chain(s) (2, 3) increase. The presence of increased concentrations of this " carbohydrate-deficient " transferrin (CDT) is a specific and sensitive biochemical indicator of recent excessive drinking (1, 4). Whether the CDT result should be expressed as the absolute amount or as the amount normalized to the total transferrin concentration has been a matter of debate (4). The present study compared three commercial immu-nological test kits for quantification of the abnormal microheterogeneity of serum transferrin observed after excessive drinking: one kit that measures CDT as an absolute amount (CDTect TM RIA; Pharmacia & Upjohn Diagnostics), 1 and two kits that measure the result relative to total transferrin [an RIA (%CDT RIA) and a turbidimetric immunoassay (%CDT TIA), both from Axis Biochemicals]. With the CDTect test, the CDT content is expressed as an absolute amount (in units/L, with 1 unit of CDT in the CDTect assay equivalent to ϳ1 mg of transferrin) of the transferrin isoforms with a pI Ն5.7. According to a recent report, the CDTect assay measures part of the asialo, monosialo, and disialo isoforms as well as traces of trisialo transferrin (5). In brief, transferrin in the serum sample is saturated with Fe 3ϩ , and the isoforms are separated on an anion-exchange chromatography microcolumn. Quantifi-cation of CDT is carried out by a double antibody RIA. Because of a gender-based difference in the baseline concentrations of asialo and monosialo transferrin (6), different upper reference limits must be applied for males (20 units/L) and females (27 units/L). The %CDT RIA test 2 also utilizes an initial ion-exchange microcolumn separation; however, the CDT result is expressed as the percentage of asialo, monosialo, and disialo transferrin relative to total transferrin. …