The ethanol test is used for both medical and legal purposes.
The goal of medical testing is to identify the presence of ethanol in order to effectively treat the patient's symptoms. For medical purposes blood and sometimes urine or breath tests are used to detect the presence of ethanol and to measure its concentration. One or more of these tests may be ordered when a patient presents to a hospital emergency department with symptoms suggesting ethanol toxicity. Symptoms may include confusion, staggering, vomiting, lethargy and unconsciousness.
Occasionally, other tests for by-products of ethanol breakdown in the body may be done, such as urine testing for ethyl glucuronide. The patient may also be tested for other types of drugs and poisons and for other medical conditions.
The goal of legal testing is to identify the presence of ethanol and to evaluate its presence in the context of a variety of different laws. Legal testing must be done by specially trained people and the handling of the sample is carefully recorded in a procedure known as chain-of-custody. Testing may be ordered to determine whether a motor vehicle driver has a blood ethanol concentration that is over the legal limit; whether someone ordered by a court not to drink ethanol has done so; and to determine whether ethanol consumption has contributed to an accident. Post-mortem ethanol testing may be done to determine whether ethanol contributed to a person’s death. Legal ethanol testing may also be performed randomly or ‘with cause’ as part of an employer's drug testing program to determine whether an employee has ethanol in their system.
Samples tested for legal purposes may include blood or breath. Breath testing is the most common test performed on drivers. It uses the tail-end sample of breath from deep in the lungs and uses a conversion factor to estimate the amount of ethanol in the blood. Blood ethanol testing may be ordered to confirm or refute findings, and/or ordered as an alternative to breath testing. A is sometimes ordered to monitor people for the presence of ethanol. Saliva (oral fluid) ethanol testing is becoming available as an alternative screening test.
In some cases people may be required to undergo regular testing to show they are limiting their ethanol intake on a long-term basis. This is done by checking the level of a naturally-occurring substance in the blood known as CDT (carbohydrate deficient transferrin), which may be increased for weeks after ethanol intake.
Medical ethanol testing is ordered to help doctors treating a patient who has symptoms that suggest intoxication with ethanol.
Legal ethanol testing may be ordered whenever there is reason to suspect that a person has not followed a drinking-related law, and whenever there has been an accident and/or unexpected death to determine whether ethanol played a role. Employment ethanol testing may be performed randomly and when the employer suspects that an employee has ethanol in their system while on the job.
For medical testing, the detection of ethanol in a sample indicates that the person's symptoms may be due to ethanol and the concentration present can give an indication of how severe the ethanol is. For legal testing, the person's result is compared to legal allowable limits.
The ethanol level measured in a breath sample gives a good estimate of a person's blood ethanol, but a positive breath test result may be checked by performing a blood test.
Breath sample concentrations can be affected by ethanol present in the mouth from consumption within the last few minutes, including the use of substances that may contain ethanol such as mouthwash and cough syrup.