Biochemical Tests

Although biochemical tests generally are less sensitive than verbal tests in screening for alcohol problems, they may prove particularly useful in identifying patients unwilling or unable to acknowledge their levels of drinking, and in corroborating findings from self-report measures. Biochemical tests also may identify relapse to alcohol use more promptly than reports by the patient.

Although measurements of ethanol in breath, blood, or urine are accurate, they reflect only very recent consumption (< 24 hours). Health care providers are typically more concerned with identifying patterns of longer-term excessive consumption. Several biochemical tests have been proposed as markers for this purpose. Gamma glutamyl transpeptidase (GGT), mean corpuscular volume (MCV), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) have been used the most. Carbohydrate-deficient transferrin (CDT) is a new marker that has the promise of having greater specificity than the others.

GGT is the most commonly employed marker to evaluate heavy alcohol consumption.
As with other biochemical tests, exact relationships between parameters of drinking such as amount, duration and history of use, and serum GGT levels have not been precisely specified. At least in chronic alcoholics, long-term daily intake of five to six drinks (64 g) can significantly elevate the GGT. Four to 5 weeks of abstinence are generally necessary to reduce an elevated GGT level in alcoholics to within normal levels. The half-life of GGT is 14 to 26 days. GGT lacks specificity for heavy drinking. Nonalcoholic liver disease, biliary tract disease, gall bladder inflammation, lipid disorders, obesity, and medications such as anticonvulsants, anticoagulants, and oral contraceptives may elevate GGT levels.

The AST, ALT, and MCV have also been used as markers of alcohol consumption. They generally are less sensitive than the GGT, and the GGT usually is the first to become elevated with heavy drinking. The MCV also is not as useful as the GGT in monitoring relapse to heavy drinking because it may take several months of abstinence for the values to return to normal.

CDT is the newest and, perhaps, the most promising biochemical marker of heavy drinking. It is at least equal to GGT in sensitivity and is more specific. The few known causes of false-positive include primary biliary cirrhosis, chronic active hepatitis, and a few rare genetic conditions. CDT is available to research laboratories but, at the present time, is not available commercially.

Transferrin is a glycoprotein with a molecular weight of 75,000 to 80,000, the function of which is to transport iron. It contains about 6% carbohydrate by weight. With excessive drinking, the carbohydrate content of transferrin may be reduced; hence, the term carbohydrate-deficient transferrin. It is unclear whether the mechanism is attributable to decreased activity of the glycosyltransferases, which add the carbohydrate groups initially to the transferrin molecule, or to an increased activity of the deglycosylating enzymes for example, sialidase which remove the carbohydrate groups. Four to seven drinks (50-80 g) per day for one week will raise CDT levels in alcoholics. On the other hand, five to seven drinks per day for 3 weeks failed to raise CDT levels above normal limits in social drinkers. CDT levels generally return to the normal range within a couple of weeks of abstinence by alcoholics. CDT has a half-life of approximately 15 days. CDT appears less sensitive as a marker for heavy drinking for women and adolescents. The reasons for this are unclear but may reflect greater heterogeneity in CDT levels among women in general and the fact that adolescents typically drink in a short, binge fashion rather than in a protracted, heavy manner.