A blood test can be used to get a very accurate blood alcohol concentration reading. However, blood tests are invasive and harder to carry out, so police departments have decided instead to rely on Breathalyzers, or breath tests. These also measure BAC, and, over the years, people have come to accept that they're accurate.
However, some studies have shown that this is not actually the case. One study compared breath test readings with blood test readings and found that they could be off by as much as 50 percent.
For example, if you're pulled over in California and the breath test says that your BAC is 0.10, it could actually be anywhere from 0.05 to 0.15. Since the legal limit is 0.08 for most drivers, this is a huge variance. If you're at 0.05, you're free to go with no consequences. If you're at .15, you're legally drunk, with a BAC nearly twice the limit, and you're going to jail.
Because of this, some have argued that it's unfair to trust breath tests at all unless they say the person's BAC is .2 or greater. This way, even if it's 50 percent off, the person's minimum BAC is still .1, which is over the legal limit. Otherwise, these experts claims, the court is just using potentially inaccurate data to take away a person's license, put him or her behind bars, and level heavy fines and fees.
If you've been accused of drunk driving and you think the test was inaccurate, leading to a false arrest, you have to know what legal options you have.
Source: National Motorists Association, "Breathalyzers Fail Legitimacy Test," accessed Nov. 15, 2016