More Than One Culprit
There are a host of other organisms that are capable of altering the blood alcohol content of a specimen. In a study involving over 100 specimens ninety-four percent of all forensic alcohol blood samples tested were found to be contaminated with viable bacteria and/or fungi, even in the presence of one percent sodium floride. In those cases where an organism that does not produce alcohol is found the sample is nevertheless suspect, because the presence of the one does not preclude the existence of the other an earlier point in time. An alcohol producing organism may have thrived for a time and died out, after which its cell walls disintegrated. In that event, it would not be detectable, but the presence of the other non-alcohol producing organism means that the sample is inherently unreliable.
In the Mix - the Powders
In addition to instrument errors contamination can compromise a result by increasing an error at an unknown rate. Preservatives and anti-coagulants, which are usually in a powder form before blood is drawn, may not be adequately mixed into the specimen. When this occurs, errors are bound to follow due to fermentation (in the case of too little or inadequately mixed preservative) or microclotting (in the case of too little or inadequately mixed anti-coagulant).