How Accurate Are Breath Test Results?

Many people in Texas may view the handheld breath testing device as the de-facto symbol for charges for driving while intoxicated. Indeed, you yourself may make the same connection. Yet this association prompts a question many have regarding breath tests: why does law enforcement choose to measure your breath to determine the alcohol content of your blood?

There obviously is a connection given the reliance on breath test results to determine intoxication. Understanding how these devices generate their measurements, however, may just provide you with the foundation needed to challenge their validity.

Breaking down the mechanics of breath testing devices

Per the Alcohol Pharmacology Education Partnership, the type of alcohol you ingest when drinking is ethanol. This compound is water-soluble, allowing it to permeate the linings of the organs of your gastrointestinal tract after ingestion to end up in your bloodstream. Once in your blood, ethanol eventually finds its way to your lungs, where it begins a gradual process of vaporization upon coming in contact with the oxygen in the lungs. This vaporized ethanol then leaves your body on your breath. Handheld breath testing devices look to this ratio of alcohol on your breath to that in your blood to come up with a blood-alcohol content measurement. To do this conversion, they assume a constant blood-to-breath ratio of 2100:1 (the alcohol content of your blood being 2100 times greater than that on your breath).

Challenging breath test results

In reality, however, your actual BAC can range between 1500:1 and 3000:1 (depending on a number of different factors). This wide range of variability calls the accuracy of breath test results into question. Some experts even believe that handheld breath testing devices may have a margin of error as high as 50% (an unacceptable degree of certainty when criminal charges hang in the balance).

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