Blood Alcohol Tests: The Hematocrit Conundrum

     Whole blood is comprised of red and white blood cells, platelets and other clotting and cellular material, dissolved salts, amino acids, fats, and water.  Those solid materials are frequently referred to as “hematocrit.”  The hematocrit level is, therefore, the percentage of the total volume of blood taken up by the solid particles.  Determining a person’s hematocrit level at the time the blood is drawn is the only way to know what the correct conversion ratio is for the person who was tested at the time of the blood alcohol test.

     The average hematocrit for men is 47% with a “normal” range between 42% and 52%.  The average for women is 42% with a range from 37% to 47%.  Studies have shown, however, that over time an individual’s hematocrit can vary by up to 15%. 

     In general, the higher the hematocrit level, the higher the reported blood alcohol concentration in a serum or plasma test, which is the kind most frequently encountered in a hospital setting.  The higher someone’s hematocrit level, the less liquid we can expect to find in their blood.  Since the alcohol will migrate or remain with the liquid portion of the blood, a person with a higher hematocrit will have a higher blood alcohol test result when that blood alcohol test is a plasma or serum test performed in a hospital. 

Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website

You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

AddThis Social Bookmark Button

One Response to “Blood Alcohol Tests: The Hematocrit Conundrum”

  1. Great post. I would like to take it one step further. These are, of course, things that you know as you and I have spoken about it many a time.

    But the other issue is the validation of the science and whether or not it meets a Frye/Daubert challenge. Hospital blood is, of course, a colormetic spectrophometric enzyme reagent reaction test (the hospital blood plasma or blood serum test).

    Preamble: As long as you see this following chart in the insert , then the argument infra is sound

    Ethyl Alcohol+ NAD+ —-> Acetaldehyde+NADH+H+

    PART ONE: The answer is there is no answer…

    First, there is absolutely no consensus in the scientific community as to the proper conversion factor. There is no number. Therefore, as there is no scientific agreement, then no number should be used by the Courts. It is a basic Daubert/Frye matter. The government as the proponent of the evidence has the burden to prove it is reliable and based on sound science. The very fact that there are studies that go as low as 1.10 overstatement to as high was 1.59 make it so. That is a 69% swing. Come on.

    The conversion factor depends on hematocrit (packed cell volume) entirely (well almost entirely, but for the sake of brevity it is the most important part). Serum or plasma (almost-one article had a statistical artifact) always over estimates BAC. Plasma actually more so. If I am forced to use a conversion factor AND THAT IS A BIG IF. I go with Professor Rainey and 1.49 which is the highest peer reviewed article that I could find as the presumption of innocence demands that we give all benefit to the accused. Also Dr. Citron has published a peer reviewed article on it.

    PART TWO: The answer is the science, the defense is the truth.

    Here is my logic proof…

    1. If you accept as true that these Hospitals perform tests on less than [whole] blood
    2. If you accept that these hospitals perform tests on blood plasma

    Then, would not the following be true…

    3. Plasma blood and serum blood are more or less the same (or best case scenario for the defense the conversion is 1:1.04 serum:plasma) according to:

    Distribution of ethanol and water between plasma and whole blood; inter- and intra- individual variations after administration of ethanol by intravenous infusion
    Jones, A.W., Hahn, R.G., Stalberg, H.P.(1990),Scandanavian Journal of Clinical and Laboratory Investigation, 50(7), Nov. 775-780.

    Comparison of plasma, serum, and whole blood ethanol concentrations
    Winek, C.L., Carfagna, M. (1987), Journal of Analytical Toxicology, 11(6), 267-8.

    4. If you accept Rainey’s assertion in Relation between Serum and Whole-Blood Ethanol Concentrations; Petrie M. Rainey: Clinical Chemistry, Vol. 39, No. 11, 1993. (pg 2288-2292)

    In that study (peer reviewed, scientifically reliable), Rainey studies the relationship between hospital (serum) blood test results and contemporaneous whole blood results. He finds that the median ratio for adjusting serum to whole blood is 1.15. The high of the range was 1.59. 1.49 for the central 99% (or 2 standard deviations) and 1.40 for the central 95%. Therefore, I like to use 1.49.
    6. The combination of 1:1.04 serum:plasma and then 1:1.49 whole blood:serum, then mathematically 1.5496 if you really want to stretch.

    That is EXCLUDING the machine’s in-built range of analytical error, control run specific drift errors, pippetting errors, etc. It also presumes no exogenous alcohol production and perfect collection, inversion, transportation, storage, preparation and analysis. You cannot presume all of those things. There is only one presumption and that is the presumption of innocence.

    Just a lazy thought on a Thursday mid-morning. Thanks for the post. This blog is a wonderful resource.

    Justin J. McShane, Esquire

Leave a Reply

You must be logged in to post a comment.