With intoximeters, what reflects the true alcohol concentration of the blood?

• A. Direct blood sample
• B. Deep lung breath
• C. Mouth alcohol sample
• D. Breath at room temperature

Answer: (B)

The essential idea is that alcohol in breath best represents what’s in the blood when the sample comes from the deep-lung air that has been in the alveoli. This end-tidal or deep-lung portion of the exhalation comes into equilibrium with the bloodstream, so its alcohol concentration mirrors the blood alcohol concentration (the blood-to-breath ratio is about 2100:1). Mouth alcohol or residual alcohol in the mouth can contaminate the sample and give inaccurate results, which is why shallow or mouth-level samples are not reliable. While a direct blood sample would provide the exact BAC, intoximeters rely on deep-lung breath because it noninvasively estimates BAC accurately. Breath measured at room temperature would distort the reading due to temperature and humidity effects, whereas properly conditioned deep-lung breath yields the true reflection of blood alcohol.