Scientific Components of DUI Testing in Maryland

The following is excerpted from an interview with a DUI attorney in Maryland. Below, they discuss chemical BAC testing (blood, urine, breath tests).

Most Common Chemical BAC Tests in Maryland

In Maryland, the vast majority of DUI cases use breath tests. Some states use blood or breath and other states use blood tests only. Not many states use urine tests. Usually a urine test is only used if the breath or blood test is not admissible for some reason. In DC, they had a breath test fiasco so they tried using a urine test, but they ran into a lot of problems with it. In Maryland, the science really applies to the breath test. If there is a serious injury caused by a car accident or vehicular homicide, then they will use blood testing and gas chromatography.

Accuracy of Chemical DUI Tests

If it’s properly done, a blood test is more accurate. There are a lot of factors that go into whether it is properly done, such as whether the blood was drawn correctly and whether it was mixed with an anti-coagulant. If all the different variables that go into the blood test are done right, then that is more accurate. The breath test is an extrapolation. They use the person’s breath to extrapolate how much alcohol is in their blood using a partition ratio. The partition ratio is the ratio of breath alcohol to blood alcohol, but they apply the same ratio to all people.

Based on the way human physiology works, there cannot be one partition ratio for everybody because people process alcohol differently based on gender, age, ethnicity, food consumption, and time of day. There is too much variation to say that everyone has the same partition ratio. The breath test is certainly less effective than the blood test. Because we don’t use urine, I don’t know enough about urine to say how effective it is. The most reliable testing for alcohol content is a blood draw, which is why Maryland requires it in cases of serious accidents and vehicular homicide cases.

Can You Request to Take the More Accurate Blood Test?

No, if someone insists on a blood test, the police will write that up as a refusal.

What Regulations Need To Be Followed For Each Chemical Test?

There are various certifications and calibration requirements. Occasionally, there will be situations in which a certain jurisdiction was not using properly calibrated equipment, so a whole group of DUI cases will get dismissed. A competent lawyer can be very helpful in situations where the machine was not properly calibrated or certified or the operator was not properly certified. A good lawyer will look at the back story of the machine, including certification records, the calibration, and the history of the machine. Sometimes when we get the discovery back on the machines it will show that it has been consistently reading people as having high or low BAC levels. We are able to request that information, which is what a good lawyer should do.