More on Hospital Blood Tests for Alcohol

In an enzymatic test, the type customarily performed when a patient is brought into the emergency room at a hospital, the analysis for alcohol concentration is typically performed on serum or plasma samples, so it is important that you do not assume that the test was performed on whole blood. To measure the alcohol concentration through an enzymatic assay test, the serum or plasma is combined with an enzyme, alcohol dehydrogenase, to form acetaldehyde. Coincidentally, acetaldehyde is the first and most important metabolite of ethyl alcohol.

During this process, nicotinamide adenine dinucleotide (NAD) is converted to NADH. The concentration of NADH is measured to determine the alcohol concentration. Plasma and serum are quite different and have different water content levels. Because alcohol distributes to the different components of the blood according to the water content, the relative water content level of plasma and serum is an important consideration.

Plasma and serum have nearly the same ratio of water to blood and should produce similar alcohol concentrations. The ratio of serum to whole blood varies widely, with at least one study showing the ifference can be as great as 49%. However, a statistical average of about 1.18 seems to be indicated.

The serum or plasma alcohol test is indirect. The amount of NADH, which is an enzyme, is measured spectroscopically at the 340 nanometer wavelength. The amount of NADH present is supposed to be proportionate to the amount of alcohol converted by ADH to acetaldehyde. However, when lactic acid is produced due to stress on muscles resulting from an injury or when ringers lactate is administered by paramedics, LAD will also react with ADH and be read as ethyl alcohol by the enzymatic tests.

In most cases these hospital reports will have “Not for Legal Purposes” written or stamped across the front. However, do not be surprised if zealous prosecutors attempt to use them, and at least in Georgia, they will usually be admissible. Therefore, defense counsel must be prepared to deal with them.


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

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