Blood Test For Drinking and Driving

Types of Tests:

Blood tests taken at a hospital or police station are the most accurate chemical sobriety evaluations used to determine the blood alcohol level of a subject. They are also, unfortunately, the least convenient and most expensive. Blood tests may be requested onsite by an officer who feels the breathalyzer test inaccurately measured a subject’s BAC.

Considered an intrusive method, a blood alcohol test can quickly determine the amount of alcohol in the blood at the time the sample is taken. Since the body continues to break down alcohol at a steady rate after drinking, the time that passes between drinking and collecting the blood sample will affect the results. Therefore, it is important to have the test conducted as quickly as possible from the time of the driving incident.

Blood alcohol tests are very accurate in determining BAC levels, but in some cases, the results may be misleading. These cases may involve:

  • People with diabetes or high blood ketones.
  • People taking cough medicines or herbal supplements.

However, the most susceptible variable in blood testing for alcohol levels is determined by the actual methodology of the blood drawing. First and perhaps most obvious, the sample is at risk of alteration by an alcohol swab before the needle is inserted. As the needle is inserted, the alcohol on the surface of the skin can actually contaminate the sample by increasing the overall amount of alcohol found in the blood.

In addition, there are two ways in which blood can be sampled for BAC levels:

  • By testing the whole blood
  • By testing just the blood serum

Testing the whole blood is standard procedure for blood alcohol tests. However, some hospitals may only test the serum. Producing a blood alcohol concentration for the blood serum sample alone may produce blood alcohol count levels up to 25% higher than whole blood results.

Overall, the ability to accurately determine blood alcohol concentration levels through blood sampling is very high. Out of all the chemical tests, it is the most successful.

The majority of drunk driving cases that involve the driver undergoing a blood sampling result in conviction if the driver is definitively above the legal limit. The evidence provided in court upon proof of a failed blood alcohol test is extremely difficult to deny.