Taking a blood test in Massachusetts after being pulled over for driving under the influence may seem like a sure way to be found guilty if someone has been drinking alcohol, or a sure way to be proven innocent if he or she has not. The truth is, though, that laboratory errors could result in either a higher or lower BAC than is actually present.

The National Association of Criminal Defense Lawyers, Inc., points out that there have been laboratory errors and scandals across the United States for years, and Massachusetts has not escaped the list. In fact, two chemists tampered with or falsified evidence on the tests of tens of thousands of people in the state. In addition to cases affected by unethical chemists, there are a number of ways that honest mistakes may be made.

According to the National Highway Traffic Safety Administration, there are many ways that a defense attorney may challenge a blood test in a DUI case. These could have to do with the medical devices used to draw, test and store the blood. For example, there could be improper packaging or a laboratory could be using equipment from a company that did not receive FDA approval on their products. The tubes used to collect the blood could have lost their vacuum seal, or they could have expired.

A perfect measurement of anything is not possible, and these variations and uncertainties are often relevant in court. When cases go to trial, a judge or jury should not be expected to rely on the chemical test alone to determine whether the defendant is innocent or guilty.