Breath Alcohol Tests in Michigan Can be 230 Percent Too High

The results obtained from breath testing instruments utilized by law enforcement in the investigation of drunk driving cases can be as much as 230 percent higher than corresponding venous blood tests fn.1. This disparity can occur because arterial blood alcohol content is higher than venous blood alcohol content during the absorption phase of the blood alcohol content curve. The consequences of this disparity are so profound that even some drivers with ostensibly shocking levels of intoxication are conceivably innocent. Understanding why this is so requires a basic understanding of what happens to alcohol in the body: its pharmacokinetics, meaning its absorption, distribution, metabolism, and excretion.

Beverage alcohol, more properly called ethanol (EtOH) or grain alcohol, is most commonly ingested orally. What follows assumes oral consumption, and this is important because different rules apply when alcohol is injected or administered rectally. (Yes, alcohol enemas were once a thing).

During oral administration, absorption begins almost immediately after drinking, in the mouth, but does not begin in earnest until the alcohol reaches the small intestine. As the alcohol is absorbed it moves throughout the body, first into the liver, then to the heart and lungs, then back to the heart before being distributed with the arterial blood circulation throughout the body. Ethanol is “hydrophilic” meaning it has an affinity with and readily dissolves in water. As the alcohol is absorbed into the bloodstream primarily from the small intestine, it is distributed throughout the total body water, and then metabolized in the liver and excreted unchanged in breath and urine.fn. 2 Let us now look at each of these steps or processes along the way.

Alcohol Absorption

The absorption of alcohol begins almost as soon as it encounters the oral mucosa.fn. 3 Although absorption of alcohol into the blood stream starts in the stomach, it does not begin in earnest until the stomach contents empty into the small intestine. In approximate numbers, 20% of the alcohol can be absorbed through the stomach lining, whereas 80% is typically absorbed through the small intestine.fn. 4 The contents of the stomach are the number one factor governing when alcohol passes into the small intestine. If the stomach is full of calorie rich foods, such as fats and proteins, this food, and therefore any alcohol, will remain in the stomach far longer compared with drinking on an empty stomach.fn. 5

Full absorption, meaning the point at which an equilibrium is reached between rate of absorption and rate of elimination usually occurs between 30-60 minutes after the last drink is consumed.fn. 6 However, some studies have shown longer, or shorter time periods are required for complete absorption. Full absorption can take place in as little as 15 minutes but may take as long as 138 minutes depending on pattern of drinking and individual differences in gastric emptying. Some studies indicate that under some circumstances complete absorption of alcohol takes a lot longer time than 138 minutes.fn. 7 The variability in full absorption is largely due to the feed or fasted state of the drinking. As will be shown, in a drunk driving case, it is imperative to know when full absorption has occurred.

Absorption of alcohol takes place by the process of simple or passive diffusion through the various membrane tissues in the body. Because of its low molecular weight and high solubility in water, ethanol passes rather easily through throughout the human body, including the blood-brain barrier.

Alcohol Distribution 

As indicated above, ethanol is hydrophilic and therefore is distributed within and throughout the human body according to the amount of water present in each respective fluid and tissue. This means that tissues with lots of water, like the brain and muscle, will “pull” a lot of alcohol out of the bloodstream, whereas tissues with little water, such as fat and bone tissue, will take up much less of the absorbed alcohol. Either way, the distribution of alcohol within the body is a relatively rapid process and depends on relative blood flow and tissue water content.fn. 8

Because alcohol is distributed by passive diffusion, if a tissue has 8% more water content than in the blood, this tissue is expected to have 8% higher alcohol content compared with the blood. It is on this basis that scientists can estimate, within certain limits, a person’s blood alcohol concentration indirectly by analysis of ethanol in other specimens, such as saliva, sweat and urine, and in cases where a death has occurred, the vitreous humor. In post-mortem tests, analysis of ethanol in eye fluid is thought to be important to determine whether a person had consumed alcohol before death.fn. 9 The opposite is also true. Knowing the alcohol concentration of a particular tissue allows a scientist to estimate the amount of alcohol in a person’s blood.

The distribution of alcohol also depends somewhat on total body water, which in turn depends on a person’s gender, age and body mass index or amount of body fat (obesity). Women and the elderly tend to have proportionally less water and more fat in their bodies compared with young men. The total body compartment for non-obese men comprises about 55–60% of body weight and for non-obese women is about 50–55% of body weight.fn. 10

Alcohol Elimination

Alcohol is eliminated from the human body through its interaction with an enzyme called “alcohol dehydrogenase” or ADH. While ADH is most heavily concentrated in the liver, it is present in other tissues of the body also, such as the gastric mucosa and the kidney. The clearance of alcohol from the blood stream during the post-absorptive elimination phase takes place through what is called “zero-order kinetics,” which means it is eliminated at a constant rate per unit time independent of the amounts ingested.fn. 11 Consequently, elimination is not dose-dependent; rather, it is enzyme dependent. This pharmacokinetic behavior is one of the main reasons blood alcohol concentrations can be deducted from units of alcohol consumed. It is also why, provided enough information is known about the subject, it is possible to calculate how long it will take for an individual to eliminate a given number of units of alcohol.

To perform these blood alcohol calculations there must first be agreement relative to the terms used and to define the amount (dose) consumed. In the US, scientists usually use “standard drinks” to define consumption of alcohol, such as one 12 oz beer (5 vol%), one 1.5 oz of 80 proof liquor (40 vol%) or one 5 oz glass of wine (12 vol%). A simple calculation shows that each of these types of drink contain almost the same quantity of ethanol of ~14 grams. Complete absorption of one of these drinks (14 g ethanol) has the potential to raise a person’s BAC by between .02 and .025 g%, depending on the person’s body weight and completeness of absorption. The easy way to calculate a BAC is therefore to assume that each standard drink increases a person’s BAC by a factor of 0.02-0.25 g%. This means that rapid consumption of four standard drinks (3-4 bottles of beer, 3-4 shots of whisky or 3-4 glasses of wine) are necessary to reach a BAC of 0.08 g%, the statutory limit for driving in most states.fn. 12

As mentioned above, zero-order kinetics also means that BAC decreases at a constant rate per unit of time, and the scientific literature shows that this rate varies from about 0.01-0.025 g% per for most people, with the average for males being 0.015 g% per hour compared with 0.018 g% per hour for females.fn. 13  Women tend to eliminate quicker than men because they have larger livers as a percentage of total body mass, and therefore proportionally more ADH enzyme available.

In the population of drinkers, the literature suggests that the range of elimination from blood start as low as 0.01 g% per hour and might be as high as 0.039 g% per hour, a nearly four-fold difference.fn. 14 Most of this difference is attributable to nutrition and genetic factors and hepatic enzyme activity. Furthermore, the person’s prior exposure to alcohol plays a role, owing to habituation and a process known as enzyme induction. This means that a naïve drinker, who is seldom exposed to alcohol, or has not had anything to drink for a long period of time, will have an elimination rate in the lower range, whereas an alcoholic who consumes large quantities of alcohol daily will eliminate at the higher range, owing to a process known as enzyme induction.  However, there are many factors that can impact a person’s elimination rate including various disease states, such as malnutrition, liver cirrhosis etc.  A. W. Jones, perhaps the world’s best-known researcher regarding the forensic aspects of alcohol, has reported that for DUI suspects, the average elimination rate from blood was 0.019 g% per hour and with a 95% range from 0.009 to 0.029 g% per h.fn. 15

Breath vs Blood-Alcohol Testing

When alcohol is consumed orally it begins its journey from the small intestine to the lungs via the hepatic vein. In the circulatory system it returns to the heart and lungs and is recirculated via arterial blood throughout the body. The exchange of alcohol into the lungs where it can be expelled into a breath test instrument occurs via the arterial blood system, and therefore, breath tests measure arterial blood alcohol content. Blood samples are uniformly withdrawn from the venous blood system. Because the BrAC time course follows more closely ABAC rather than VBAC, breath-tests for alcohol will tend to overstate VBAC whenever marked A-V difference exist.fn. 16

Because alcohol passes from the digestive system into the blood stream via passive diffusion, as beverage alcohol is consumed and collected in the stomach and small intestine, a person’s BAC will increase until the amount of alcohol in the blood is greater than the amount of alcohol in the gastro-intestinal tract. There will be a brief period of equilibrium, and thereafter, a person’s BAC will begin to decrease.

Because of the way alcohol moves through the body, during the absorptive phase arterial blood has a higher ethanol concentration than venous blood returning to the heart. This means that a breath test will generally be higher than a simultaneous venous blood test during the absorption phase. During the elimination phase, the opposite will be true, the breath alcohol test will be lower than a corresponding blood alcohol test (venous blood). The only time it would be expected that both tests would be the same is during the brief period at point of equilibrium at about 30-60 min after end of drinking.fn. 17

How is This Science Relevant to the Defense of Allegedly Intoxicated Drivers?

In the 1970’s, when the states began passing per se laws, the crime was a function of blood alcohol content. As Jones points out, a “tricky situation emerged because the drunk driving statutes were defined in terms of BAC although most of the alcohol measurements for legal purposes were made in breath. It was therefore deemed necessary to convert the measured breath concentration into a presumed blood concentration.”fn. 18 The legal solution to this scientific problem was to change the law so that per se violations were based on either breath alcohol or in most instances bodily alcohol content.fn. 19  On first blush it may appear therefore that the difference between breath and blood alcohol is irrelevant, and this may be true as it relates to the UBAL theory of DUI. But what about the OUIL or common law theory? Here again most state law provides that a chemical test result can be considered by the fact finder and given whatever weight it deserves in considering the common law theory. Consequently, if the government wishes to submit both theories to the jury then this information remains relevant.

Having established the relevance, the reason this is all so significant in DUI prosecutions is that breath alcohol concentration follows arterial blood alcohol, whereas for legal purposes alcohol is determined in samples of venous blood from drivers. Making an arterial puncture is a riskier procedure and needs specially trained phlebotomists. Because of this mismatch between arterial and venous BAC, Jones indicates that the venous breath-blood ratio is a moving target. One study has shown that arterial breath alcohol tests can overestimate venous blood alcohol concentrations by more than 100% for a significant amount of time after drinking stops. The maximum deviations found for four individual subjects were +230%, +190%, +60%, and +30%.fn. 20

These unacceptably large deviations demonstrate that quantitative evidential breath alcohol test results are to a suspect’s disadvantage compared with if venous blood was taken for analysis if the testing was during a rising BAC (absorption phase) and prior to complete absorption and distribution of alcohol in the body water compartment.

Jones has further stated in several publications, “The arterial and venous blood-alcohol profiles are shifted in time owing to the time it takes for alcohol to equilibrate between arterial blood and tissue water. Alcohol is metabolized in the liver and not in the muscle tissue, which acts as a reservoir for alcohol. The concentrations of alcohol in arterial and venous blood were the same at only one timepoint, which signifies complete equilibration of alcohol in total body water. During the entire post-absorptive phase, the concentration of alcohol in venous blood draining skeletal muscles is slightly greater than the concentration in the central arterial blood; therefore, the arterial-venous BAC differences become negative.”fn. 21

How to Use This Information in Your Next DUI Trial

As with any issue related to science, there are at least two ways to enter this information into evidence. Through the State’s expert or through your own expert. Most prosecutors will not call a witness in a breath test case possessing the requisite knowledge necessary as a predicate to your cross-examination. Look at the complaint or information and determine if any witnesses with a science background are contained therein. If so, have several copies of your articles and be ready to cross-examine using them like any learned treatise. For tips on the strategic use of MCR 707, see Steve Goran’s excellent Michigan Bar Journal Article entitled Cross Examination Using Learned Treatises.fn. 22

Another potential witness is your client, but calling the defendant to the stand carries more inherent risk than cross-examining a state’s expert. Nevertheless, you will need to know and be able to establish your client’s drinking pattern on the day and/or evening of the offense. Your expert will need this information too. Consequently, as part of your initial case work-up, a careful client interview will be required. Determine if others witnessed your client’s drinking and establish whether bar or restaurant receipts can be obtained.

Best practices would suggest hiring your own expert. This remains true even when your client cannot afford to hire one herself. In fact, the mistaken belief that your client will not qualify for public funds to hire an expert because he had retained counsel may be considered ineffective assistance of counsel.fn. 23 A well-qualified toxicologist would be able to testify to virtually everything contained in this article and hopefully do so in a way that your jurors will be able to understand.

Be ready to meet the relevance objection of the prosecutor. As discussed above, you may wish to concede that the theory is not relevant to the UBAL theory of OWI. You will also need to educate your judge as to why this information remains relevant to the OUIL theory.

Unfortunately, the anti-drunk driving public policy is so strong that our courts and our legislators continue to tie our hands when it comes to raising scientifically sound defense to breath and blood testing. This should not deter zealous defense counsel from continuing to raise them.

by Patrick T. Barone, Esq.

Patrick T. Barone is the CEO & founding partner at the Barone Defense Firm. With offices in Birmingham and Grand Rapids, the criminal defense Firm primarily handles intoxicated driving cases and those involving firearms and criminal sexual conduct in the State and Federal Courts. Mr. Barone has an “AV” (highest) rating from Martindale-Hubbell, and since 2009 has been included in the highly selective US News & World Report’s America’s Best Lawyers while The Barone Defense Firm appears in their companion America’s Best Law Firms. Mr. Barone is an adjunct professor at the Western Michigan University/Thomas M. Cooley Law School and the author of five books including the two-volume treatise Defending Drinking Drivers, which is considered a seminal work on the topic. Additionally, he has authored more than 100 legal articles and many book chapters on a variety of criminal defense topics. Mr. Barone is a popular speaker, and frequently teaches legal concepts, trial skills and forensic science to others at national and state conferences, workshops and seminars attended by lawyers, judges, doctors, and scientists. He has also provided expert commentary in newspapers, on television and on radio. Patrick is a graduate of the Gerry Spence Trial Lawyer’s College and is also a psychodrama TEP (Trainer, Educator and Practitioner). He is the only Michigan lawyer so certified. In this capacity he provides trial skills training and personal growth workshops in conjunction with the Michigan Psychodrama Center.  He can be reached at


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