Measuring Blood Alcohol Levels: Hospital Procedures

Blood alcohol level is the amount of alcohol present in a sample of blood, usually measured in milligrams of alcohol per 100 millilitres of blood. This is often referred to as blood alcohol concentration (BAC). Hospitals may use blood tests to measure blood alcohol levels, particularly in emergency situations, such as suspected alcohol poisoning. However, there are questions surrounding the accuracy and reliability of hospital blood alcohol tests, especially when used in legal contexts, such as driving under the influence (DUI) cases. While hospitals typically test serum or plasma, which can yield higher ethanol concentrations than whole blood tests, legal BAC calculations require whole blood measurements.

Blood samples are taken from a patient's arm using a needle

To measure blood alcohol level, doctors use a needle to draw blood from a patient's arm. This process is also known as a blood alcohol test. Blood samples are taken from a patient's arm using a needle by a medical professional, such as a doctor or a hospital phlebotomist. This procedure is generally safe, although slight pain or bruising may occur at the site of the needle insertion. These symptoms typically disappear quickly.

Blood alcohol tests are used for both medical and legal reasons. For medical purposes, the test can be used to check for alcohol poisoning, a life-threatening condition that occurs when blood alcohol levels become very high after consuming large amounts of alcohol. This test can also be performed on young children who may have ingested household products containing alcohol, such as mouthwash or certain cold medicines. Additionally, doctors may order a blood alcohol test if a patient arrives at the hospital unconscious, confused, or displaying other signs of heavy drinking. The test helps medical professionals understand the patient's condition and determine the best course of treatment.

In terms of legal reasons, blood alcohol tests are often used to determine if an individual has been driving while intoxicated. Police officers may request a breathalyzer test, but a blood test can also be required if the individual refuses the breathalyzer or in cases where there is suspicion of drunk driving or underage drinking. Blood tests provide more accurate results than breathalyzers. Additionally, employers may use blood alcohol tests for pre-employment screening or to check for on-the-job drinking, especially if a work accident has occurred.

The blood sample drawn from the patient's arm is typically tested in a hospital laboratory. The blood tubes are either allowed to sit so that the red blood cells separate and clot, or they are centrifuged to separate the solid cellular components from the liquid portion of the blood. The liquid portion, known as plasma or serum, is then used for testing. The serum or plasma sample contains a higher concentration of alcohol than a whole blood sample since alcohol is soluble in water, and serum is mostly water.

While hospital blood alcohol tests are useful for medical purposes, they may not be considered scientifically reliable for legal or forensic purposes, especially in cases involving driving while intoxicated (DWI) or vehicular assault/homicide prosecutions. This is because the tests may not distinguish between ethanol (alcohol) and other substances that can produce false-positive results. Additionally, hospitals typically test serum or plasma, while legal BAC calculations require the use of whole blood.

BAC is calculated using a plasma (serum) blood sample

Hospitals typically measure blood alcohol levels using a blood test, breath test, or urine test. Blood alcohol concentration (BAC) is a measure of alcohol in the blood, usually expressed as a percentage. It is calculated in grams per 100 mL of blood, so a BAC of 0.08 means your blood is 0.08% alcohol by volume.

The BAC of the serum blood is usually listed in the reports under “ETOH (ethanol) Lvl (level) 0.—% HI (high)..” The plasma test will produce a result that is more than 10–15% higher than a whole blood test drawn at the same time. For example, a .10 serum/plasma alcohol concentration converted to a whole blood alcohol concentration would result in a higher whole blood alcohol concentration.

The EIA process is quick, with results available within approximately 20 minutes. However, it is not forensically reliable due to its inability to specifically measure ethanol and its high likelihood of false positives. In Germany, BAC is determined by measuring the serum level and then converting to whole blood by dividing by the factor 1.236, although this method underestimates BAC by 4-10% compared to other methods.

Serum is mostly water, so there is a higher concentration of ethanol in serum than in whole blood

Hospitals typically perform blood plasma (serum) tests instead of testing whole blood. Serum is the liquid portion of a blood sample after the solid cellular components have been removed. This is because serum is mostly water, and ethanol (the main ingredient of alcoholic drinks) is water-soluble. Therefore, there is a higher concentration of ethanol in serum than in whole blood.

However, this method of testing has limitations. For example, in cases of driving while intoxicated (DWI), the prosecution requires a whole blood alcohol concentration for conviction. This is because the exact conversion rate between serum ethanol levels and whole blood ethanol levels is impossible to accurately predict. Serum testing may also produce false positives, as the enzymes used in the test react to other substances in addition to alcohol.

To address these limitations, law enforcement typically obtains a blood sample for forensic analysis by responding to the hospital where the suspect is being treated. The hospital phlebotomist draws the blood, and the samples are transported to a forensic laboratory for analysis. This ensures that the blood alcohol content (BAC) is accurately determined and can be used as evidence in legal proceedings.

In summary, while hospitals often use serum testing to evaluate a patient's condition and prescribe medications, whole blood testing is necessary for forensic and legal purposes, such as determining blood alcohol content for a DWI conviction.

EIA testing is quick but not forensically reliable

Blood alcohol content (BAC) is the amount of alcohol in one's blood, which is developed from drinking beverages that contain alcohol. BAC tests are used for a variety of reasons, including medical testing, legal testing, and employment. Medical testing is used for diagnosing alcohol poisoning, monitoring alcohol use disorder, and checking for symptoms of intoxication. Legal testing is used for determining if a person is driving under the influence, underage drinking, or drinking while on parole. Employers may also test for alcohol use before hiring someone.

One way to test BAC is through the use of an EIA test. EIA testing is a quick process that can provide hospital serum results within approximately 20 minutes. While EIA testing is widely accepted for clinical applications and achieves clinical and diagnostic objectives, it is not forensically reliable for a DWI or criminal prosecution where a blood alcohol level needs to be proven beyond a reasonable doubt. This is because EIA tests are cross-reactive, meaning they identify the presence of NADH regardless of the underlying substance that may have created its presence. This can often lead to false-positive results, which is the worst scientific result. For example, lactate, which is often infused in a saline IV to act as an acidosis buffer, will trigger a lactate metabolic process that produces NADH, exactly like ethanol metabolism. Thus, the EIA test cannot distinguish the source of the NADH and may report an incorrect level of ethanol.

Furthermore, serum is mostly water, and since ethanol is water-soluble, there will be a higher concentration of ethanol in serum than in whole blood. This is problematic in criminal prosecutions since only a whole blood BAC expression is permitted. Although the serum ethanol level can be "converted" to a whole blood ethanol expression, the exact conversion rate is impossible to accurately predict.

Therefore, while EIA testing is quick and effective for clinical and diagnostic purposes, it is not suitable for forensic purposes where blood alcohol levels need to be proven beyond a reasonable doubt.

Blood alcohol tests are used to check for alcohol poisoning

Blood alcohol content (BAC) is the term used to describe the amount of alcohol in a person's blood. BAC levels can range from 0% to over 0.4%. A BAC of over 0.40% is considered a potentially fatal blood alcohol level, which can result in a coma or death from respiratory arrest. BAC levels are typically reported as a percentage, such as 0.03% BAC. They can also be listed as grams per millilitre (g/mL), for example, 0.03 g/100 mL.

A blood alcohol test is carried out by a healthcare professional, who will take a blood sample from a vein in the patient's arm using a small needle. The blood is then collected into a test tube or vial. The process usually takes less than five minutes, and results can be available within 20 minutes or a few hours, depending on the laboratory.

In addition to a blood alcohol test, other tests may be ordered to check a patient's overall health if alcohol poisoning is suspected. These can include an electrolyte panel blood test, liver function tests, and an electrocardiogram (EKG) to check the heart.

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