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Why can breath and blood tests be wrong?

On Behalf of | Feb 23, 2024 | OVI Defense

When individuals talk about breath and blood tests, they often think of them as reliable indicators of certain substances in their bodies. However, these tests can sometimes be inaccurate, leading to potentially serious consequences.

It is important to understand why these tests can go wrong to ensure fair outcomes.

Mistaken sources

Breath tests, commonly used to measure blood alcohol concentration, or BAC, rely on the assumption that the alcohol content in the breath is directly proportional to that in the blood. However, several factors can influence the accuracy of these tests.

For instance, leftover alcohol in the mouth from recent consumption or certain medical conditions such as acid reflux can artificially inflate BAC readings. Moreover, improper calibration or usage of the breath device can lead to erroneous results.


Similarly, blood tests, while considered more accurate than breath tests, are not foolproof. Factors such as contamination, improper storage or equipment malfunction can all contribute to inaccurate readings.

Additionally, the metabolism of certain substances varies from person to person, affecting the concentration levels detected in the blood. Even slight errors in sample collection or analysis procedures can lead to significant differences in the results.

Inherent limitations

These tests provide only a snapshot of a person’s state at the time of testing and may not always reflect their true condition. For example, someone who has just consumed alcohol may register a high BAC even though they are not intoxicated, while others may exhibit impairment despite having a lower BAC.

Drinking is a common activity in many social situations, and it does not always lead to a high BAC.  By acknowledging these tests’ limitations, people can strive to improve the reliability of these tests and uphold the principle of justice.