An official test used to track heavy long-term alcohol consumption. When alcohol is consumed steadily and heavily (4-6 units of alcohol per day) for several weeks, the CDT % increases, and this continues if you continuously drink heavily.
Occasional or binge drinking also raises CDT levels, depending on how often and how much is consumed. Reducing alcohol consumption results in a drop in CDT levels, which normalise in a few weeks. This test is very specific, meaning that it is not affected by other substances. Authorities use it as an official test to evaluate harmful alcohol use.
Read more about the CDT