Ethanol

What is being measured?
This test measures the amount of ethanol in the blood, breath or saliva. Ethanol (also called ethyl alcohol or alcohol) has been consumed by civilisations all over the world for thousands of years. Small amounts of ethyl alcohol can cause euphoria, relaxation and reduced inhibition. Moderate amounts can cause impaired judgement and reduced motor skills; large amounts over a relatively short time can cause acute ethanol toxicity, with disorientation, depressed breathing, coma and even death. Chronic consumption of large amounts of alcohol can lead to alcoholism and permanent liver damage.
When ethanol is consumed, it is absorbed from the gut and carried around the body in the bloodstream. Small amounts of ethanol are excreted in the urine or breathed out through the lungs, but most is metabolised by the liver. The liver treats ethanol as a toxin. With the help of enzymes, the liver oxidises the alcohol first to acetaldehyde, then to acetate and finally to carbon dioxide and water. The liver can process about one drink an hour, one drink being defined as the amount of ethanol in 12 ounces of beer, 5 ounces of wine or 1.5 ounces of whisky. A person who drinks more than one drink an hour will build up ethanol in the bloodstream.

How is it used?
When is it requested?
What does the result mean?
Is there anything else I should know?

How is it used?
Ethanol/alcohol testing is used for both medical and legal purposes. Samples and results for each use are usually collected and tested separately.

Medical: the purpose of medical testing is to detect alcohol so that patients with symptoms can be treated effectively. For medical purposes, alcohol tests are used to detect ethanol and measure its concentration in the blood and sometimes in the urine. One or more of these tests may be requested when a patient arrives at A&E with symptoms suggesting ethanol toxicity. Symptoms can include confusion, staggering, vomiting, lethargy and unconsciousness. Other tests, such as a full blood count, glucose and electrolytes, are often requested at the same time, as a variety of other conditions can cause similar symptoms. Further tests for drugs and for other, more toxic types of alcohol (such as methanol and isopropyl alcohol) may also be carried out if the use of other substances is suspected.

Legal: the purpose of legal testing is to detect alcohol and assess its presence in the context of different laws. Legal testing must be carried out by specialised staff and must have a strict chain of custody (a paper trail recording the transport and handling of the sample).

The test may be requested to determine whether a driver has a blood alcohol concentration above the legal limit, whether a minor has been drinking alcohol, whether someone on parole has abstained from alcohol, and whether alcohol consumption 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 carried out at random or “for cause” as part of a drug of abuse testing programme, to check whether an employee has alcohol in their bloodstream. It may also be part of the tests carried out when applying for life insurance. (These uses are considered legal testing because they require chain-of-custody documentation.)

Samples tested for legal purposes may include blood, breath, urine and/or saliva. The breath test is the most common test carried out on drivers. It uses the end of the breath sample, from deep in the lungs, and applies a conversion factor to estimate the amount of alcohol in the blood. A blood alcohol test may be requested to confirm or dispute a result, and/or as an alternative to the breath test. A urine test may also be carried out as an alternative. Usually a person collects and discards a urine sample and then collects a second sample 20-30 minutes later. The amount of alcohol in the first sample varies because it is not known how long the urine has been in the bladder. The second sample reflects a timed sample, and a different conversion factor can then be used to estimate the blood alcohol concentration. A random urine sample is sometimes requested to screen people for alcohol. Saliva alcohol testing is not often used, but may be used as an alternative screening test.

When is it requested?
Medical ethanol testing is requested when a patient has symptoms suggesting intoxication and/or ethanol toxicity. Legal ethanol testing may be requested when there is reason to suspect that a person has broken the law relating to alcohol consumption, and when there has been an accident and/or an unexpected death, to determine whether alcohol played a role. Workplace alcohol testing may be carried out at random and when the employer suspects that an employee has alcohol in their bloodstream at work. Insurance testing is mainly carried out when a person is applying for a policy.

What does the test mean?
For medical testing, detecting ethanol in a sample indicates that a person has probably been drinking, and the concentration present can give an indication of how severe the ethanol toxicity is. Symptoms and complications can vary significantly from person to person, depending in general on their state of health, age and other medicines or drugs they are taking. The ability to clear alcohol from the body also depends on the availability of the necessary enzymes and on the patient’s liver function. For legal testing, the results are compared with the legal limits.

Is there anything else I should know?
Ethanol results from different types of sample are not interchangeable. Breath and urine samples are considered good estimates of blood alcohol concentrations in most people but can be affected by a variety of factors. Urine concentrations are lower than blood concentrations. Urine samples containing both glucose and microorganisms (as can happen in people with diabetes) should not be left at room temperature for long periods, because the microorganisms present can 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-hydroxytryptophol), may be measured to assess this and confirm the ingestion of ethyl alcohol. An increased 5-HTOL/5-HIAA ratio may indicate alcohol consumption. Breath sample concentrations can be affected by alcohol consumed in the last few minutes, by ketones (released into the breath by some people with diabetes) and by other products containing alcohol, such as mouthwashes and cough syrups