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Blood Test Doesn’t Quite Add Up

Since the advent of these no refusal weekends, I’ve been seeing strange blood numbers. They are extremely high, even into the 20’s, which if true would evidence a brutally drunk client. The problem is that all the evidence accumulated prior to the DWI arrest doesn’t necessarily back up these numbers.

Clients will tell me they only had three or four beers prior to being pulled over. The blood test, which is supposed to be more precise than the breath test, doesn’t correlate. So what is happening?

Blood testing involves the use of gas chromatography. A blood sample is injected into a bottle by a technician. The sample is heated up so that vapor is created, and this vapor is injected into the machine along with a known quantity of sample gas. This combination is pushed through a column in the machine that separates the gas at different rates. When the gas hits the detector on the other side, a computer creates a result printout that identifies how much time elapsed for the gas to reach the detector. Alcohol is identified because it takes a known specific time to get to the detector.

Breath machines work through infrared spectroscopy. It shines a specific light frequency through a breath sample and records how much light is absorbed at the wavelength that alcohol affects. It has its own problems, but it is a simple, automated procedure. The cop takes the suspect to the machine and has him blow two times at intervals the machine instructs by a light and beeper. It spits out a result afterwards. The testing is immediate and case specific.

A blood test involves much more human interaction, and therefore creates more potential for human error. The officer will take the suspect to a hospital, emergency center or police lab for blood to be drawn. The nurse, technician or doctor will draw the blood. The blood is placed into a container. Then the blood is handed between officers long before it gets to the lab. The blood is likely to make its way to a police lock box at some point. Sometimes, it sits in the officer’s car for days before it is delivered. At the lab, the blood sits amongst hundreds of other samples until the lab technician retrieves it. The technician tests dozens of blood samples at the same time. Each one has different numbers assigned to them by different parties in the process. At any point in this human process, a mistake can be made that will contaminate or confuse the blood sample taken in the case.

Hopefully, jurors will be cautious in automatically believing blood test results. Often times during discovery or cross-examination, I am able to identify where the problem lies. However, even in those situations where the erroneous blood test remains a mystery, the jury should be cautious of believing all that the analyst at the police lab says. We are all thoroughly familiar of the recent shut down of the FBI lab and Houston Forensic Lab for failure to maintain proper protocol. Their mistakes caused untold damage both to accused citizens and the prosecution. it is up to the Criminal Defense Bar to keep them honest!

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