Breath vs. Blood

Updated: May 31


In Iowa prosecutions for OWI, otherwise known as driving under the influence, or, DUI in other states, the preliminary breath test (PBT), a field sobriety test, and the more accurate and admissible Datamaster DMT breath tests are measured in grams of ethanol per 210 L breath. A blood test is measured in grams of ethanol per 100 mL or 10 dL of blood. A urine test is measured in grams of ethanol per 67 mL of urine. I’m a lawyer not a scientist.

However, I once argued successfully that a blood test is more accurate than a breath test. The reason, I submitted, was that we want to know the effects of alcohol on the brain, not on the lungs. Therefore, to understand the effects on the brain, we have to measure the alcohol that is going through the brain and that does not happen directly by way of our lungs.


Under Iowa law, however, the prosecutor is free to argue that eight one-hundredths (.08) grams of ethanol in 210 L breath/100 mL blood/67 mL urine is all the same for purposes of measuring BrAC, BAC, and UAC respectively. In other words, when we’re talking about the presumptive level of intoxication at or above .08 grams in any one of the above bodily media, all are equal pursuant to Iowa Code § 321J.1 et seq.


So what’s the bottom line? This matters if law enforcement asks, for example, for a Datamaster DMT and the test subject invokes the right to an independent chemical test at his or her own expense. The idea being that the test subject doesn’t trust the accuracy of the machine, either in general or specific to the example being used to do the testing. It’s their right, then, to request a second opinion by way of a blood test, for example. In my case, the blood test was under .08 while the Datamaster test was at .08. These are unusual circumstances. But they can happen. And it’s important to understand metabolization of alcohol in either consenting to a test or refusing. Once a test subject consents, he or she may also ask for the independent chemical test. It’s not an option if the test subject refuses all testing.

If you or a loved one has been charged with OWI (DUI) in the State of Iowa, contact us for a free consultation today.


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