ethanol (Ethyl alcohol, Blood alcohol, Blood EtOH)
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p396-397
2025-12-09
26
Type of test Blood; urine; gastric; breath
Normal findings
Blood: 0-50 mg/dL, or 0%-0.05%
Possible critical values
Blood: > 300 mg/dL
Test explanation and related physiology This test is usually performed to evaluate alcohol-impaired driving or alcohol overdose. Proper collection, handling, and storage of blood alcohol are important for medicolegal cases involving sobriety. Legal testing must be done by specially trained people and must have a strict chain of custody (a paper trail that records sample movement and handling).
Samples tested for legal purposes may include blood, breath, urine, or saliva. Blood is the specimen of choice. Blood is taken from a peripheral vein in living patients and from the aorta in cadavers. Results are given as mg/dL, g/100 mL, or a percentage. Each represents the same amount of alcohol. Blood alcohol concentrations (BACs) greater than 80 mg/dL (0.08%) may cause flushing, slowing of reflexes, and impaired visual activity. Depression of the central nervous system occurs with BACs over 0.1%, and fatalities are reported with levels greater than 0.4%. Persons with BACs less than 0.05% are not considered under the influence of alcohol. Levels greater than 0.05% are considered in most states to be illegal for the operation of motor vehicles and as definite evidence of intoxication.
For legal purposes, when outside of a laboratory or hospital, taking a blood sample for later analysis in the laboratory is not practical or efficient. Breath testing is the most common test performed on automobile drivers. It uses the tail end sample of breath from deep in the lungs and uses a conversion factor to estimate the amount of alcohol in the blood. Blood alcohol testing may be ordered to confirm or refute findings. Alcohol that a person drinks shows up in the breath because it gets absorbed from the intestinal tract into the bloodstream. The alcohol is not metabolized on first pass through the liver. As the blood goes through the lungs, some of the volatile alcohol moves across the alveolar membranes and is exhaled.
Urine testing may also be performed as an alternative to blood. Usually, a patient collects and discards a urine sample and then collects a second sample 20 to 30 minutes later. Saliva alcohol testing is not as widely used but may be used as an alternate screening test. Alcohol stays in the saliva for 6 to 12 hours. Finally, hair testing is used but represents a more chronic use of alcohol.
Interfering factors
• Elevated blood ketones (as with diabetic ketoacidosis) can cause false elevations of blood and breath test results.
• Bacteria in the urine of diabetic patients with glucosuria can metabolize the glucose to alcohol.
• Alcohols other than ethanol (e.g., isopropyl [rubbing alcohol] or methanol [grain alcohol]) will cause positive results.
* The use of alcohol-based mouthwash or cough syrup may cause false positives on a breath test.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: gray or red
• Follow the institution’s chain-of-custody protocol.
• Follow the agency’s protocol regarding specimen collection.
• Use a povidone-iodine wipe instead of an alcohol wipe for cleansing the venipuncture site.
• If a gastric or urine specimen is indicated, approximately 20 to 50 mL of fluid is necessary.
• Breath analyzers are taken at the end of expiration after a deep inspiration.
• The exact time of specimen collection should be indicated.
Abnormal findings
Alcohol intoxication or overdose
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