Ethanol, Blood

Quantitation of alcohol level for medical or legal purposes; test unconscious patients; used to diagnose alcohol intoxication and determine appropriate therapy; detect alcoholism and to monitor ethanol treatment for methanol intoxication. Must be tested as possible cause of coma of unknown etiology since alcohol intoxication may mimic diabetic coma, cerebral trauma, and drug overdose.

Ethanol is the single most important substance of abuse in the United States. It is the active agent in beer, wine, vodka, whiskey, rum, and other liquors. Ethanol acts on cerebral function as a depressant similar to general anesthetics. This depression causes most of the typical symptoms such as impaired thought, clouded judgment, and changed behavior. As the level of alcohol increases, the degree of impairment progressively increases.

Ethanol is absorbed rapidly from the GI tract. Peak blood levels usually occur within 40 to 70 minutes on an empty stomach. Food in the stomach can decrease the absorption of alcohol. Ethanol is metabolized by the liver to acetaldehyde. Once peak blood ethanol levels are reached, disappearance is linear; a 70 kg man metabolizes 7−10 g of alcohol/hour (15±5 mg/dL/hour). The urine:blood ratio is considered to be about 1.35:1 but is quite variable. The average saliva:blood ratio is 1:20. Symptoms of intoxication in the presence of low alcohol levels could indicate a serious acute medical problem requiring immediate attention. The half-lives and effectiveness of certain drugs (eg, barbiturates, etc) are increased in the presence of ethanol.

References:

Simpson G. Accuracy and precision of breath-alcohol measurements for a random subject in the postabsorptive state. Clin Chem. 1987 Feb; 33(2 Pt 1):261-268. PubMed 3802510