Biochemical markers of alcohol consumption have shown promise as objective measures of alcohol consumption. CDT is an abnormal transferrin profile that is caused by sustained heavy drinking [
6]. While the results have varied, CDT is typically elevated after 50–80 g of ethanol (i.e., 3.5–6 US standard drink units) consumed daily or almost daily over 14 days [
7], with all but the heaviest drinkers returning to normal after four weeks of abstinence [
8]. Disialotransferrin is one of the minor glycoforms of human transferrin, and the percentage of total CDT that is disialotransferrin, as determined by high-performance liquid chromatography (HPLC), is the recommended method for measuring %CDT [
9]. The percent of abstainers and moderate drinkers combined that tested %CDT positive (i.e., the percent false positive, or one minus the specificity of the test) using a cutoff of 1.8% was 0% in Italy [
10] and Sweden [
9] and 5.6% in a multi-national study [
6]. In the latter study, the specificity was 100% when moderate drinkers were excluded, and the authors noted that errors in self-report were likely among the moderate drinkers [
6]. The sensitivity of %CDT for detecting heavy drinking at the 1.8% cutoff in that study was 44.6%. Despite this low sensitivity, we chose %CDT because of its high specificity as well as its ability to be quantified in plasma. Other candidate biomarkers include phosphatidylethanol, which is highly sensitive and specific but currently only available for testing in whole blood [
11], and traditional markers such as γ-glutamyl transpeptidase and mean corpuscular volume which are widely available but also lack sensitivity [
11], and are subject to alterations due to HIV disease and ART use.