BLOOD TESTING ERRORS

Category:

(That really happens?)

by

George Scharmen
315 Dwyer
San Antonio, Texas 78204
(210) 226-8021

Blood testing for alcohol using chromatography is supposed to be the gold standard for forensic evidence of intoxication.  Much of the time it is, but yes, in a significant percentage of the tests there are laboratory, machine or analyst errors.  For example, the laboratory may receive blank or erroneous chain of custody documentation, but it may nevertheless enter record data indicating that there is an accurate chain of custody.  This information must be correct because the substance being tested (your blood) has unique characteristics such as your name, your DNA and your alcohol concentration, if any.  Therefore, it is important for your lawyer to confirm the validity of the outside of the lab chain of custody of the blood tube so as to be sure the laboratory number assigned to the blood tube should be named for you. Obviously, it should not be someone else’s blood in your name!

Another problem frequently occurring is machine error.  This equipment is used every day: day in and day out – morning, night and weekends.  It’s complicated because it’s actually two machines attached together by gas tubes, software and a printer.  There is also a “carrier gas” (hydrogen) connected to the machines constantly flowing through the equipment that is needed to push the samples through for testing.  It comes from a hydrogen generator.  There is one generator for three machines.  So, the software breaks down during the automated testing process.  The hydrogen generator fails.  Needles used to inject the gas into the system malfunction or break.  There are many other things that can affect the machinery.

Analysts have a tedious job taking a hundred or more blood tubes out of the refrigerator.  They open the tubes and document the notes on the seals to confirm them with the receiving documentation.  They pipette a specific amount of the blood and an internal chemical standard in each testing vial.  The vial must have a septum for the needle to puncture, and they are sealed with a crimped aluminum top.  The vials are placed in sequence in a rotary tray for testing.  This process may take a few hours to complete.  The analysts make pipetting errors when they put the wrong amount of fluids in the vials.  They make mistakes on their bench memoranda documenting the chain of custody.  They fail to correct measurement errors in their controls.  They fail to inject any fluid at all in a vial.  They put too much or too little fluid in the vials.  They may also attempt to hide their errors.  Sometimes they take measurements of a control from another testing batch and insert those numbers in the batch being tested in order to make it look correct.

Some of this sounds strange and frightening, but I have seen all of these errors.  In fact, in preparation for a lecture I have been reviewing about 50 of my prior cases to see what percentage of the blood tests had errors.  I am only about sixty percent through the process, and the numbers are really shocking –even to me.  So, I am telling you that your lawyer must not simply look at a laboratory result and say: “well, you failed.”  That number is meaningless unless the test was done correctly.  From where I sit, there appears to be 50% chance that something went wrong during your test.


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