Blood alcohol test
This test measures the amount of alcohol, or ethanol, in your blood.
When you drink alcohol, more than 90 percent of it is processed by your liver. The rest leaves your body in your urine, sweat, and breath. Ethanol moves rapidly from your gastrointestinal tract – mostly your stomach – and is absorbed into your bloodstream. Your blood alcohol level continues to rise for 30 to 90 minutes after you have your last alcoholic beverage.
This test is used by law enforcement agencies and hospitals to find out the concentration of alcohol in a person's blood. In an adult or teen, it can be used if a driver may be driving under the influence. In children, it can be used to check for alcohol poisoning.
Although alcohol poisoning can be fatal, most such deaths are accidental. Besides wine, spirits, and beer, ethanol is found in a surprising number of common household items. Young children sometimes get alcohol from:
Perfume, cologne, and body sprays
Over-the-counter cough, cold, and allergy medications
Most cases of alcohol poisoning in young children are caused by drinking cologne or mouthwash.
If you suspect that a young child has swallowed alcohol from any household source, seek medical help right away. Call the poison control center immediately at 800-222-1222 or 911.
You may have this test if a police officer suspects you of driving under the influence. A breath test, or analysis, gives faster results, but a blood test is more accurate.
You or your child may also have this test if your doctor suspects alcohol poisoning. Teens and youth are at particular risk for binge drinking, which can cause alcohol poisoning. If an adult or child comes to the ER unconscious, or appears drunk or disoriented, this test is used to determine the ethanol concentration in the blood.
If you are in the ER, your doctor may also order other tests to screen for chronic alcohol toxicity. The tests may include:
Serum glucose, to check your blood sugar level
Serum electrolytes, to check for dehydration
Complete blood count, to look at the major parts of your blood
Blood urea nitrogen and creatinine, to check how your kidneys are working
Head CT scan, to check for head trauma or stroke
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Blood alcohol concentrations are expressed in different ways. Law enforcement agencies use grams per deciliter (g/dL), and health care professionals use milligrams per deciliter (mg/dL) or, in some instances, millimoles per liter (mmol/L). For example, the legal limit for ethanol concentration can be stated as 0.08 g/dL, 80 mg/dL, or 17 mmol/L.
Here are some blood alcohol concentration levels and what they do to your body:
0.00 g/dL – Sober
0.03 g/dL – May feel a slight buzz, but without having trouble talking, seeing, or keeping your balance
0.05 g/dL – Feeling buzzed or relaxed
0.08 g/dL – Legally drunk in the U.S. You may have trouble balancing, talking, and seeing straight. If you are a frequent drinker, you may not have any symptoms of blood alcohol poisoning at this point, but damage to your brain and liver are still occurring.
0.10 g/dL – Impaired judgment, decreased attention, trouble walking, and mood changes
0.15 g/dL – Blackouts and lack of physical control
0.20 g/dL – "Sloppy drunk," vomiting, confusion, staggering around
0.30 g/dL – Unconscious, stupor
0.40 g/dL – Coma or possible death
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Timing is important. Having this test too soon or too long after drinking alcohol can affect your results. The test is only accurate within a six- to 12-hour window.
You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.