cohol consumption cross-sectionally is blood alcohol concentration,  which can also be used to
judge tolerance to alcohol. For example, an individual with a conc entration of 150 mg of
ethanol per deciliter (dL) of blood who does not show signs of intoxication can be pre-
sumed to have acquired at le ast some degree of tolerance to  alcohol. At 200 mg/dL, most
nontolerant individuals demons trate severe intoxication. 
Regarding laboratory tests, one sensitive la boratory indicator of heavy drinking is a
modest elevation or high-normal levels (>35  units) of gamma-glutamyltransferase (GGT).
This may be the only laboratory  finding. At least 70% of indi viduals with a high GGT level
are persistent heavy drinkers (i.e., consuming ei ght or more drinks daily on a regular basis).
A second test with comparable or even higher levels of sensitivity and specificity is carbo-
hydrate-deficient transferrin (CDT), with levels of  20 units or higher us eful in identifying in-
dividuals who regularly consum e eight or more drinks daily. Since both GGT and CDT
levels return toward normal within days to weeks of stopping drinking, both state markers
may be useful in monitoring abstinence, espe cially when the clinician observes increases,
rather than decreases, in thes e values over time—a finding indicating that the person is
likely to have returned to heavy drinking. The combination of tests for CDT and GGT may
have even higher levels of sens itivity and specificity than eith er test used alone. Additional
useful tests include the mean corpuscular volume (MCV), whic h may be elevated to high-
normal values in individuals who drink heavily— a change that is due to the direct toxic ef-