How accurate are blood, breath and urine tests?

On Behalf of | Oct 16, 2018 | DUI/DWI

When the police pull you over on suspicion of a DWI, the officer will likely ask you to perform a breath test, known as a breathalyzer. Law enforcement often use breath tests as a way to determine the level of intoxication of a driving individual, but there are other ways this can be determine.

Blood and urine tests can also indicate levels of intoxication, but breath tests are the most convenient, which is why use them during a DWI stop. If they end up arresting you for driving while intoxicated, you may be wondering how accurate these blood alcohol content (BAC) tests are.

Blood test

This test is the most accurate of all three tests, but typically medical professionals need to perform a blood draw in a clinical setting, which may not always be available. There are ways that blood tests could end up being inaccurate, such as if the lab that tested the blood made an error.

Breath test

Law enforcement considers devices that test the breath fairly accurate, but there is room for inaccuracy. Breath tests are portable, and individuals do not need to be in a sterile setting to perform the test. This makes it a convenient option for police officers, as many states have implied consent laws. These laws state that an individual pulled over on suspicion for a DWI has consented to chemical testing.

There are factors that can alter the results of a breath test, making it read as a higher BAC than it should. Factors that affect breathalyzer results include:

  • Medications
  • Medical conditions such as diabetes or acid re-flux
  • Diet
  • Body temperature
  • Burping

Urine test

This test is the least accurate of the three, which is why law enforcement often uses the test as a last resort. Alcohol can take a longer amount of time to reach the bladder than the bloodstream, and when it does reach the bladder, if you do not urinate, it could stay in the bladder for a longer amount of time. Both factors can skew BAC results.

When police pull you over and test your breath, or have your blood or urine tested, it is important to remember that there is room for error. Because of this, you could make a defense against the accuracy of the chemical testing.