Blood Test Defenses

Obviously, blood is the most accurate way to obtain a BAC. However, there are many things that can go wrong, and various inaccuracies are often present. Typically, I break the errors down into three categories. Error’s by the officer, phlebotomist, and analyst/crime lab.


11.2.1 The Officer’s Role

The officer’s role typically will begin by asking for a blood test. Usually, blood is drawn at the hospital. And usually, it is taken because the person was injured, otherwise has to go to the hospital, or the local police department’s breath machine is broken or no certified operator is available. Although blood is more accurate, it costs the police more to obtain, so they typically will not do it unless they have to.

At the hospital, the officer will often use a “blood kit”, which he usually has in his police vehicle. Part of the kit should include grey top tubes (grey topped tubes have anti-coagulants & preservatives in them; sodium fluoride and/or potassium oxalate), and a swab typically of povidone iodine (so that an alcohol swab or other swab is not used).

The officer then gives the kit to the phlebotomist, and is eventually given it back after the blood is drawn. Either the officer, or the phlebotomist, should label the tubes. The officer’s job is then to transport the blood to the lab to be analyzed. Sometimes, the officer will bring it to the police station and leave it there for a few days or more. Even worse, often times it is not put in a refrigerator.

Practice Note: Look at the chain of custody form to see what the officer did with the blood, and where he stored it.


11.2.2 The Phlebotomist

The phlebotomist is the person who actually drew the blood. 

The phlebotomist should use a swab/cleanser that will not interfere with the BAC analysis. Some examples of things that probably shouldn’t be used are alcohol, soap, and possibly water.

The phlebotomist should use a grey topped tube as it contains an anti-coagulant & preservative.

The phlebotomist should invert the tube 6-7 times so that the anti-coagulant/preservatives mix with the blood. If you can, try to obtain through discovery any other directions/instructions the phlebotomist should have given. They are sometimes included in the blood kit. You will also want to try and determine the expiration date of the tubes that were used.

Practice Note: Make sure in your demand for a certifying scientist you also demand the presence of the phlebotomist.


11.2.3 Chain of Custody

Chain of custody issues usually go to the weight of the evidence, unless the chain of custody has incredible gaps in it, in which case it could go to foundation and admissibility

Although the prosecution has the obligation "to establish the chain of custody. . . this does not mean that everyone who laid hands on the evidence must be called." "[G]aps in the chain of custody normally go to the weight of the evidence rather than its admissibility."[6].


11.2.4 Headspace Gas Chromatography – How the Blood was Analyzed

There are two types of Gas Chromatography (GC); direction injection and headspace GC. Direct injection inserts part of the blood into the inlet of the gas chromatograph. Headspace GC measures the vapor above the blood sample (Again based upon Henry’s law). 

The GC separates the components of a mixture. Accordingly, it is a separation science.

The following is a very simple overview of how the process works. You may want to consult with an expert witness. Alternatively, the State’s witness, the analyst, will usually be more than happy to explain everything the machine does in order to show how accurate it is. However, you may then be able to show how complicated it is, and show all the potential places an error can occur.

In the simplest comparison, the GC is a fancy oven with a tube, thermometer, clock, and flame.

The blood (or headspace gas) is inserted into the GC through an injection port. The sample is heated to a high enough temperature that it is vaporized. The vapor is then mixed with a carrier gas and goes through a column[7]. The column is a tube about the width of a human hair, around 30 meters in length, usually in a coil shape, and is heated to 60 degrees Celsius[8].

As the compound moves through the column, the machine determines how long it takes to go from the beginning to end. This is referred to as the retention time. The theory behind the science is that different chemicals will take different times to reach the end.

“The column is designed to capture and slow molecules.[9]

As the compounds leave the column, they enter a flame ionization detector (FID). The molecules strike the flame and are vaporized. “The burnt and ionized particles stick to an oppositely charged detector which counts them by measuring the electrical energy as each ion hits[10].” The machine measures the signal. The size of the signal is related to how many of the particles are detected. So, the more particles, the higher the BAC. The machine compares this to a known “standard”, in order to make its calculations. The GC then makes calculations and charts the results on a chromatogram. 

The GC processes numerous samples in what are called batches, or “runs.” At the beginning of the run, the machine is given a couple samples of a known quantity of alcohol. Other samples in a run include blood from your client, other driver’s blood samples, blanks, and known samples at the end of the run. 

During every run, the computer will re-learn what a sample looks like based upon the known concentrations. By comparing the retention time against the known standard, the machine can determine what compound it is (ie ethanol) (qualitative analysis). By using the BAC of the known sample, the GC calculates the amount of the substance that is present(quantitative analysis).


11.2.5 The Lab Analyst/ Certifying Analyst

The Lab analyst is the person who ultimately analyzes the blood. Briefly, that process is to take the blood from the refrigerator, let it get to room temperature, set up the run, perform the run, look at the chromatograms, and determine the BAC.

You are entitled to have present at trial the actual person who analyzed the blood, not a certifying scientist, or other person who looked over the paperwork[11].

[6]  Melendez-Diaz v. Massachusetts, 129 S. Ct. 2527 - Supreme Court (2009)

[7]Bartell at, 16-5

[8]Garriot’s at 412

[9]Garriot’s at 413

[10]Garriot’s at413

[11] Bullcomingv.New Mexico, 564 U.S. ___ (2011).