Challenging a DUI Serum Blood Test

You’ve been pulled over for a possible DUI. You’re taken in for a blood test and it comes back that your Blood Alcohol Content (BAC) is above a .08%. End of story, right? Wrong. What people don’t realize is that different laboratories are approved by the state for different kinds of testing. Specifically, some labs are approved for testing on whole blood. Other labs are certified for testing of serum. What does this mean for you when challenging your DUI case?

When looking at lab paperwork, it’s vital that you check to see what the lab is approved to test and then confirm that that is indeed what they tested. For instance, if the lab where your blood was tested is approved for whole blood testing, make sure that’s what they tested. If they performed a serum test, you automatically have a challenge to that bloodwork, as they can only perform the test they’re approved for. If they’re approved for serum testing and that’s what they tested, there are very specific things the Commonwealth must show in order to prove their case.

First, a little scientific background. What’s the difference between a whole blood test and a serum test? When a lab performs a whole blood test, the lab tech literally just takes your blood sample and puts it directly into the machine. A serum test is different. Some labs use machines that are not able to handle a whole blood sample; the sample is too dense and will clog the machine. Therefore, because of the machine they use, they are only approved to test on serum. To do this, the lab tech will take the sample, place it in a centrifuge, and essentially spin it until the blood components are separated. The serum from the blood ends up at the top of the test tube. Rather than put the entire blood sample through the machine, the lab tech takes a sample of just the serum and runs that through the machine. Because serum is less dense than whole blood, the BAC that’s calculated will be higher than what your actual whole blood BAC is, and that’s the number we’re concerned with. To get to a whole blood BAC, the machine then uses a conversion factor to convert the serum BAC to a whole blood BAC. That number is what’s used to charge you with DUI. But how do you challenge the number that comes from the serum test?

First and foremost, don’t stipulate to the lab work. Make them bring in the technologist to testify. Why? Because there are very specific things they must prove in order for the BAC generated to be sufficient to prove DUI. The Commonwealth has to show more than a generated number and a conversion factor used. Under Commonwealth v. Karns, they have to show that the conversion factor is scientifically reliable and that it’s generally accepted in the scientific community. Commonwealth v. Renninger also states that it isn’t enough that a machine is used and that the lab is approved for the testing; more testimony is needed regarding the conversion factor.

What I’ve done in several of my cases is argued that the witness the Commonwealth brings in (the lab technologist) must be qualified as an expert in order to testify about conversion factor. Usually, the lab tech has very little advanced education and minimal, if any, advanced knowledge about conversion factors. Because it’s a scientific concept that requires more knowledge than the average layperson, I argue that any testimony about conversion would be expert testimony. Because of the lab tech’s limited knowledge base, they usually can’t meet the requirements for expert qualification. Therefore, if they can’t testify about conversion, they can’t meet the requirements of Karns and Renninger.

Some judges will refuse to qualify the lab tech as an expert and won’t allow them to testify about conversion factor. If that happens, you’re golden. Without that testimony about scientific reliability and acceptance, the Commonwealth can’t meet their burden. If you do end up with a guilty verdict, you’ve set your case up perfectly for appeal. I have run into a judge or two, however, that will say that conversion testimony is not expert testimony and allow the lab tech to blindly testify about scientific reliability and acceptance. In that situation, create a record! You need to gear up for appeal. Make sure you get all your arguments on the record, cite to published case law, force the prosecutor to put on record what they’re using to support their argument that the testimony should be allowed, and make sure the judge clarifies on the record the reasons for his decisions. In at least one county, they’ve relied on unpublished, non-precedential case law to override the binding case law. This is an abuse of discretion and will absolutely help you in winning on appeal.

Of course, this isn’t the only way to challenge the bloodwork. You should always look at the chromatograms and look for things like contamination, machine malfunction, etc. But especially in cases where the chromatograms are acceptable or for people who may not know enough to analyze them, this is a much simpler way to challenge serum blood tests. It takes the argument in a different direction when you need a more unique or out-of-the-box idea for challenging a blood result. Even if you don’t prevail at trial, you can set your case up for a successful appeal. Just be prepared with your arguments, case law, and basis for your objection, and you’ll greatly increase your chances of obtaining a successful outcome.


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