Blood Alcohol Concentration

Specimen Required

Fasting Required

Purpose of the Test

To find out if a person has drunk alcohol and to measure the amount of alcohol present in the body

When this test is required

Medical ethanol testing is used when a patient has symptoms that suggest intoxication and/or ethanol toxicity, such as flushed face, glassy or watery eyes, slurred speech or drowsiness. Medical testing may also be done on a regular basis to ensure that a person being treated for alcoholism is not continuing to abuse alcohol.Legal ethanol testing may be requested whenever there is reason to suspect that a person has not complied with a drinking-related law, and whenever there has been an accident and/or unexpected death – to determine whether alcohol played a role. Employment alcohol testing may be performed randomly or when the employer suspects that an employee has alcohol in their system while at work.

What the Test Detects

This test measures the amount of ethanol in the blood, urine, breath, or saliva. Ethanol (also called ethyl alcohol or alcohol) is the intoxicating ingredient in alcoholic drinks such as beer, wines and spirits. Small amounts of alcohol can cause excitement, relaxation, and decreased inhibition, but can also cause poor judgment and impaired eye-hand coordination; large amounts in a relatively short period of time can cause rapid…This test measures the amount of ethanol in the blood, urine, breath, or saliva. Ethanol (also called ethyl alcohol or alcohol) is the intoxicating ingredient in alcoholic drinks such as beer, wines and spirits. Small amounts of alcohol can cause excitement, relaxation, and decreased inhibition, but can also cause poor judgment and impaired eye-hand coordination; large amounts in a relatively short period of time can cause rapid alcohol poisoning with confusion, slow breathing, coma, and even death. Consumption of large quantities of alcohol over a long period of time can lead to alcoholism and to several medical problems such as permanent liver damage, cardiovascular problems, depression and anxiety. When alcohol is drunk, it is absorbed by the stomach and intestine, and carried through the body in the bloodstream. Small amounts of alcohol are removed by the kidney in urine or breathed out from the lungs, but most is broken down by the liver. Alcohol is poisonous to the liver. With the help of enzymes, the liver oxidizes the alcohol first to acetaldehyde, then to acetate, and then finally to carbon dioxide and water. The liver can process about one unit of alcohol an hour – with one unit of alcohol being defined in the UK as 10 mL (8 grams) of pure alcohol, roughly equivalent to 250 mL (half a can) of beer or lager, 80 mL (half a 175 mL glass) of wine (12% alcohol by volume), or a single measure (25 mL in England) of spirits. A person who drinks more than 1 unit of alcohol an hour is likely to build up alcohol in their blood stream. See MoreSee Less

Preparation for the Test

No test preparation is needed. Measured breath alcohol concentrations may be invalid if alcohol has been consumed orally within 15 minutes of the test due to the presence of alcohol in the mouth.

Sample Requirements

A blood sample is obtained by inserting a needle into a vein in the arm; a breath sample is collected by blowing into a tube attached to a measuring device. Urine samples are collected in plastic containers; sometimes a single urine sample is collected and sometimes two separate samples may be collected with the first discarded and the second collected after a measured time. Saliva samples may be collected from the mouth using a swab.

Additional Notes

Results from different types of ethanol sample are not interchangeable. Breath and urine samples are good estimates of blood alcohol concentrations in most people but can be affected by a variety of factors. Breath sample concentrations can be affected by alcohol consumption immediately before the test, 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 due to the delay in excreting alcohol. Peak concentrations in urine are reached approximately 45-60 minutes after alcohol ingestion. Urine samples that contain both glucose (such as may be seen in diabetics) and bacteria or yeast, should not be left at room temperature for long periods of time because the glucose can ferment and produce ethanol. Fermentation can also be seen in post-mortem samples. Occasionally two other tests are used which measure serotonin metabolites, 5-HIAA (5-hydroxyindoleacetic acid) and 5-HTOL (5-hydroxytryptophol), which can help confirm whether alcohol was drunk. An increased ratio of 5-HTOL/5-HIAA can indicate alcohol consumption.Children may develop low blood sugar (hypoglycaemia) in association with alcohol poisoning, so health practitioners may request blood glucose tests along with ethanol concentrations if they suspect ethanol toxicity in children.

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