The ethanol test, commonly known as alcohol test, is used for both medical and legal purposes.Samples and results for each use are usually collected and tested separately.

Medical: medical testing is used to determine the level of ethanol in the blood in order to effectively treat the intoxicated person's symptoms. Blood is the most common sample used for medical alcohol tests. The tests may be ordered for a person who presents to the emergency room with signs and symptoms suggesting ethanol toxicity.

Other tests, such as a complete blood count (CBC), glucose, and electrolyte measurement, are often ordered at the same time because there are a variety of other conditions that can cause symptoms similar to ethanol intoxication.

Overdose testing, drugs of abuse testing, and testing for the presence of other toxic alcohols such as methanol and isopropyl alcohol may also be performed if a person is suspected of ingesting or using other substances.

Legal (Forensic): legal testing is used to identify the presence of alcohol and to evaluate its presence in the context of a variety of different laws.Legal testing must have a strict chain-of-custody.Testing may be ordered to determine, for example, whether:

• A driver has a blood alcohol concentration (BAC) that is over the legal limit
• An under-age minor has been drinking
• Someone on parole has abstained from alcohol
• Alcohol consumption has contributed to an accident

Post-mortem ethanol testing may be done to determine whether alcohol contributed to a person's death.

Legal ethanol testing may also be performed randomly as part of an employer's drug testing program or it may be performed "with cause" as part of an investigation after an on-the-job accident has occurred.It may also be done as part of an application for life insurance. These uses are considered legal alcohol tests because they require chain-of-custody documents.

Samples tested for legal purposes may include blood, breath, urine, and/or saliva.Breath testing is the most common test performed on drivers.It uses a conversion factor to estimate the amount of alcohol in the blood.

Blood ethanol testing may be ordered to confirm or refute findings and/or ordered as an alternative to breath testing.Urine testing may also be performed as an alternative.Usually, a person collects and discards a urine sample and then collects a second sample 20 to 30 minutes later.The amount of alcohol in the first sample will be variable because it is unknown how long the urine has been in the bladder.The second sample will reflect a timed sample and a conversion factor can then be used to estimate blood alcohol.A random urine sample is sometimes ordered to monitor people for the presence of alcohol.Saliva alcohol testing is not as widely used but may be used as an alternate screening test.

Medical ethanol testing is ordered when a person has signs and symptoms that suggest intoxication such as:

• Bloodshot, glassy, or watery eyes
• Flushed face
• Droopy eyelids
• Blank stare or dazed look
• Twitching or body tremors
• Thick, slurred, or loud speech
• Rambling train of thought
• Unusually fast or slow talking
• Slow response to questions or comments
• Repetitive or irrational statements
• Lethargy, drowsiness or falling asleep
• Vomiting

With higher blood ethanol levels, more serious signs and symptoms may appear. These may include:

• Confusion, stupor
• Staggering
• Irregular (long gaps between breaths) or slow breathing(less than eight breaths a minute)
• Unconsciousness
• Seizures
• Blue-tinged skin or pale skin
• Low body temperature (hypothermia)

Medical testing may also be done on a regular basis to ensure that a person who is being treated is not continuing to abuse ethanol.

Legal ethanol testing may be ordered when there is suspicion that a person has not followed a drinking-related law and whenever there has been an accident or unexpected death.Employment alcohol testing may be performed randomly and when the employer suspects that an employee has alcohol in his or her system while on the job.Insurance testing is primarily performed when someone is applying for a policy.

For medical testing, the detection of ethanol in a sample indicates that a person has likely been drinking, and the concentration present can give an indication of the degree of intoxication.Symptoms and complications may vary significantly from person to person. The individual's general health, age, and other medications or drugs that he or she is taking can all affect an individual's symptoms.The ability to clear the alcohol out of the body also depends on the health and function of the person's liver.

For legal testing, results obtained are compared to legal allowable limits.

The table below lists some possible interpretations of blood ethanol results:

Someone who chronically consumes significant amounts of ethanol can develop a tolerance to it and may show fewer signs and symptoms and visible impairment at a higher blood alcohol level than someone who does not consume ethanol as often.

Different ethanol sample results are not interchangeable.Breath samples are considered to be good estimates of blood alcohol concentrations in most people but can be affected by alcohol consumption within the last few minutes, ketones, released into the breath by some diabetics and dieters, and by other substances that contain alcohol, such as mouthwash and cough syrup.

Urine concentrations lag behind blood concentrations. Peak urine alcohol levels are reached 45 to 60 minutes after alcohol ingestion, at which time levels are typically about 1.3 times greater than the corresponding blood alcohol concentration, but this can be affected by various factors. Sometimes two separate samples may be collected with the first discarded and the second collected after a measured time (20-30 minutes) and tested for ethanol. This practice provides better correlation between urine and blood ethanol levels.

Urine samples that contain both glucose and bacteria or yeast (such as may be seen in some diabetics) should not be left at room temperature for extended periods of time as there is the potential for the microorganisms present to ferment the glucose in the sample and produce ethanol.This can also be seen in post-mortem samples.Occasionally, two serotonin metabolites, 5-HIAA (5-hydroxyindoleacetic acid) and 5-HTOL (5-hydroxytryptphol), may be tested to evaluate this phenomenon and confirm ethyl alcohol ingestion. An increased ratio of 5-HTOL/5-HIAA can be indicative of alcohol consumption.

Children frequently develop low blood sugar (hypoglycemia) along with ethanol poisoning, so health practitioners may order blood glucose tests along with ethanol tests if they suspect ethanol toxicity in youngsters.