A New Approach to Quantitate Carbohydrate‐Deficient Transferrin Isoforms in Alcohol Abusers: Partial Iron Saturation in Isoelectric Focusing/Immunoblotting and Laser Densitometry

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Abstract
Carbohydrate‐deficient transferrin (Tf) represents a significant advance over previous markers of alcohol abuse. Isoelectric focusing (IEF) analysis of affinity‐purified Tf, under conditions of total iron saturation, identifies a major isoform at pi 5.4 in both normal consumers and alcohol abusers; three additional Tf isoforms (pi 5.6,5.7, and 5.8) are associated with alcohol abuse. Under conditions of partial iron saturation, IEF analysis of affinity‐purified Tf reveals up to seven isoforms (pi range 5.3–6.0) common to normal consumers and alcohol abusers; three additional transferrin isoforms (pi range 6.1–6.3) are present in 68% (15/22) of the alcohol abuser specimens, but in only 8% (1/12) of the specimens from normal consumers and in none of the three specimens from abstainers. These three diagnostic bands comigrate with a set of defined Tf isoforms: human iron‐free Tf containing two sialic acid residues, human sialic acid‐free Tf with one iron molecule, and human sialic acid‐free, iron‐free Tf. Serum specimens from normal consumers and alcohol abusers, analyzed for Tf isoforms by an lEF‐immunoblot method under conditions of partial iron saturation, expressed Tf isoforms similar to those found using affinity‐purified Tf in standard IEF. Visual examination of the immunoblots reveals the diagnostic bands in 67% (32/ 48) of patients with histories of sustained alcohol abuse compared with only 17% (8/48) of the normal consumers. Scanning densitometry and volume integration analysis of the immunoblots representative of normal consumer and alcohol abuser populations results in mean (±se) values of 4.1 ± 0.8 and 19.3 ± 3.6 units, respectively (p < 0.0002).

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