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If Your Blood Sample Ferments Before It’s Analyzed, It Produces…Alcohol!


In a post a few days ago, I discussed the necessity of adding an anticoagulant to blood samples taken in DUI cases to avoid an elevated blood alcohol result due to clotting. I also mentioned in that post that if a preservative were not also added to the sample, fermentation can take place. That prompted a number of queries about fermentation in blood alcohol analysis….

Blood is an organic substance and, like any organic substance, will decompose because of enzymes and bacterial action. One of the results of decomposition is that alcohol is created in the blood. In a blood sample originally containing no alcohol, decomposition and resulting fermentation can cause a reading far above the legal limit, depending upon the stage of decay. To stop or at least slow down this process, a preservative (commonly sodium fluoride) is added to the sample; it should also be refrigerated until analyzed by the crime lab.

The amount of preservative, of course, must be sufficient, and it must be actively mixed into the blood sample. While it is common among law enforcement agencies to use 20mg of sodium fluoride, many experts view this as insufficient. See, for example, Dick and Stone, “Alcohol Loss Arising from Microbial Contamination of Drivers’ Blood Specimens”, 34 Forensic Science International 17 (1987). Further, although labs often take a week or more before receiving and analyzing blood samples, normal levels of sodium fluoride will render the sample stable for only about two days. Kaye, “The Collection and Handling of the Blood Alcohol Specimen”, 74 American Journal of Clinical Pathology 743 (1980).

To complicate things further, not all microorganisms are affected by sodium fluoride. As researchers have discovered, one such microbe that is commonly found in the human body is Candida albicans:

It has been shown that several microorganisms occasionally found in blood specimens are capable of producing ethyl alcohol. Although (one study) found that sodium fluoride effectively inhibited alcohol production from a variety of microorganisms, one – Candida albicans — appeared to be unaffected by the addition of sodium fluoride. C. albicans is commonly found in man, usually in the oral cavity and digestive tract, and less commonly in the vaginal tract of women…. The legal ramifications of this are obvious. If an oganism common to man is capable of producing ethyl alcohol in stored blood, the question arises: Are the results of alcohol analysis reflective of an individual’s level of intoxication or of possible fermentation?    

Change and Kollman, “The Effect of Temperature on the Formation of Ethanol by Candida albicans”, 34(1) Journal of Forensic Sciences 105 (1989). 

So, for those wondering, “If I’m arrested for DUI, should I take a breath test or a blood test?”, the answer is….neither is reliable — although breath is clearly the least reliable. Coagulation and fermentation are just two of many problems inherent in blood analysis for alcohol. For an example of another, see “How do I know the Blood They Tested as Mine?”. But I’ve written many posts about the unreliability of breath testing as well, such as: “Breathalyzers — and Why They Don’t Work”; “Why Breathalyzers Don’t Measure Alcohol”; “The Mouth Alcohol Problem”; and “How to Fool the Breathalyzer”.

Take your choice…..The results will probably be “close enough for government work”.

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