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Breathalyzer Accuracy vs Blood Test: What is More Accurate?

While blood tests are generally considered more accurate, breathalyzers serve as a quick and accessible method for estimating blood alcohol concentration in situations such as roadside testing for DUI. However, for legal purposes or precise alcohol level measurement, blood tests are typically relied upon due to their higher accuracy and reliability.
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C.L. Mike Schmidt Published by C.L. Mike Schmidt

How a Breathalyzer Works and What it Measures

According to Medical News Today, a breathalyzer test serves as a reliable tool for measuring Blood Alcohol Concentration (BAC), indicating the percentage of alcohol present in a person’s bloodstream. This metric enables authorities to assess the degree of intoxication [1].

Following alcohol consumption, the body absorbs this chemical through the stomach lining into the bloodstream. As blood passes through the lungs, some alcohol evaporates and moves into the lungs.

The concentration of alcohol in the breath correlates with that in the blood. Utilizing a partition ratio, BAC can be swiftly determined from exhaled air, eliminating the need for a blood sample. The typical ratio of breath alcohol to blood alcohol is approximately 2,100:1, meaning that about 2,100 milliliters (ml) of breath contain the same alcohol content as 1 ml of blood.

By applying the partition ratio, a breathalyzer calculates an individual’s BAC. Generally, this device operates on a chemical reaction principle. Alcohol vapor in the breath reacts with a potassium dichromate solution, causing it to change color from orange to green. This color alteration generates an electrical current, which the breathalyzer interprets to ascertain the BAC value.

In the United States, the standard BAC limit is 0.08%. However, in Utah, this limit is reduced to 0.05%. For adults, a BAC of 0.08% typically corresponds to the consumption of four or more drinks (usually five or more for males) within a two-hour period. A BAC measurement of 0.08 indicates that there are 0.08 grams of alcohol per 100 ml of blood or that the blood is 0.08% alcohol.

Why are Alcohol Blood Tests Used?

According to HealthLine, an alcohol blood test serves as a reliable method to confirm recent alcohol consumption and quantify the amount of alcohol ingested [2].

These tests are conducted for various legal purposes, including:

  • Assessing whether an individual was driving under the influence of alcohol.
  • Determining if a person was consuming alcohol while underage.
  • Establishing intoxication levels following a motor vehicle accident.
  • Fulfilling conditions of probation or parole.
  • Supporting criminal investigations.
  • Conducting pre-employment screenings.
  • Verifying alcohol consumption while on the job.
  • Diagnosing alcohol poisoning and administering appropriate medical treatment.
  • Monitoring participants in alcohol treatment programs.

A blood alcohol test is done at a lab. If you need to take one, you’ll be asked to go to a medical facility to have your blood drawn. This process is longer than the breathalyzer alcohol test many people associate with alcohol testing in situations like driving under the influence. However, blood tests are known to be more accurate.

How Long Does Alcohol Stay in Your System?

Alcohol detection tests utilize different mediums to assess its presence in the body. Blood tests, for instance, can detect alcohol in the bloodstream for up to 12 hours. Breath tests have a detection window of 12 to 24 hours, while urine tests can detect alcohol for 12 to 24 hours, with prolonged detection possible (up to 72 hours or more) following heavy alcohol consumption.

Saliva tests offer a detection window of up to 12 hours, whereas hair tests have an extended detection period of up to 90 days. It’s worth noting that the half-life of alcohol, the time it takes for its concentration in the body to decrease by half, is approximately 4 to 5 hours.

These detection times are approximate and can vary based on individual factors such as metabolism, hydration levels, and frequency of alcohol consumption.

Body System Time in System
Blood Up to 12 hours
Breath 12-24 hours
Urine 12-24 hours; 72 hours or more after heavier use
Saliva Up to 12 hours
Hair Up to 90 days

BAC Level Chart

The following chart summarizes different BAC levels and their potential effect on a person’s perceptions and capabilities:

BAC level Effect on perceptions and capabilities
0.01–0.05 relaxed, a slight “buzz,” less inhibited, and alert
0.06–0.10 emotional, numb, sleepy, reduced memory and coordination
0.11–0.20 mood shifts, mania, inappropriate behavior
0.21–0.30 aggression, depression, impaired vision and reasoning
0.31–0.40 unconsciousness or coma
0.41 and over potentially fatal

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If you feel affected by any of these matters, contact our criminal defense attorney today.

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