A breath test detects only what its particular instrument and protocol are designed to measure. An alcohol breathalyzer measures ethanol in exhaled air; a clinical urea breath test looks for a labeled gas produced after a patient takes a test mixture. An alcohol reading does not reveal whether someone has taken other drugs, and no single “breathalyzer” tests for every substance or disease.
How does a breathalyzer work?
An alcohol breathalyzer measures ethanol in breath. Evidential instruments sample expired alveolar air—the air from the lungs’ air sacs. The result is a breath alcohol concentration (BrAC): a measurement of ethanol in breath, not a direct measurement of blood. The UK Home Office describes evidential instruments as measuring ethanol in expired alveolar air.
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Different instruments can use different measurement principles
Some devices use a fuel-cell sensor, which oxidizes ethanol and measures the resulting electrical signal. Infrared instruments measure absorption features associated with ethanol. These are different approaches; a device does not necessarily use both. The precise technology and approval status depend on the instrument, so consumer screening devices should not be treated as equivalent to evidential equipment.
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Screening and evidential devices have distinct roles. In the United States, the National Highway Traffic Safety Administration (NHTSA) distinguishes preliminary breath-test (PBT) devices used in roadside investigations from evidential breath-test (EBT) devices built to agency specifications and used to produce results for court. A screening result is not automatically equivalent to a result from a jurisdiction-approved evidential instrument.
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| Test type | What it measures | Purpose and context | How to interpret it |
|---|---|---|---|
| Preliminary breath test (PBT) | Ethanol in breath | Handheld roadside screening in the United States, as described by NHTSA | A screening result; not automatically equivalent to an evidential result |
| Evidential breath test (EBT) | Ethanol in expired breath, including alveolar air | Forensic alcohol measurement using equipment that meets the relevant jurisdiction’s requirements | Evidence within the instrument’s approved use and the applicable procedure |
| H. pylori urea breath test | Labeled carbon dioxide in breath after a labeled urea mixture | Clinician-directed diagnostic testing using baseline and post-dose breath samples | A disease-related metabolic signal interpreted in its clinical context |
Approval is jurisdiction-specific. The Home Office’s technical requirements and approved-instrument information apply to evidential use in Great Britain; NHTSA’s specifications and conforming-product lists apply in the United States. Neither authority’s list is a universal approval list.
Can a breathalyzer detect drugs other than alcohol?
No. NHTSA states that PBT, EBT and passive alcohol screening devices are designed to identify alcohol and cannot detect drugs other than alcohol. An alcohol breath test therefore cannot establish whether someone has taken another drug. Nor does an alcohol reading, by itself, measure impairment across different people, drugs or medical conditions.
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How does a urea breath test detect H. pylori?
A urea breath test uses a different chemical question from an alcohol breathalyzer. In the PyloPlus system, the patient first provides a baseline breath sample, drinks a mixture containing labeled urea, and provides a second sample about 20 minutes later. The instrument assesses the second sample for an increase in labeled radioactive carbon dioxide. An increase is a sign of H. pylori infection, according to the FDA’s PyloPlus overview; clinicians consider the result alongside the patient’s medical history.
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The FDA describes PyloPlus as a clinician-used test prescribed by a doctor. Its 2024 supplement overview gives an indication for people aged three years or older when a doctor suspects H. pylori infection. Those details apply to that system and indication, not automatically to every medical breath test.
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- DOT/NHTSA COMPLIANT - Designed to meet the rigorous standards of expert blood alcohol screeners, from roadside law enforcement to hospital employees & treatment professionals, the Element is compliant with US DOT & NHTSA regulations for alcohol screening devices.
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There is no universal disease breathalyzer
Other diagnostic breath tests may use different substrates, instruments and target gases. The FDA’s overview of diagnostic breath-test combination products gives examples including tests for H. pylori, gastric-emptying disorders, carbohydrate malabsorption and intestinal bacterial overgrowth. These are separate applications, not conditions identified by one all-purpose device.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why calibration and quality controls matter
A forensic alcohol result depends on more than the device’s sensor: the instrument must be maintained and checked under the applicable program. NHTSA describes quality-assurance plans that specify inspection, maintenance, calibration and recalibration intervals, with records kept for those activities. Calibration units provide known ethanol-vapor concentrations for calibration checks.
Quality systems also include laboratory and program competence. NIST’s OSAC standards library lists ANSI/ASB Standard 153-23, a 2023 standard for proficiency testing in forensic toxicology laboratories and breath alcohol programs. The listing supports the importance of proficiency testing; it does not make different jurisdictions’ rules interchangeable.
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Quick Recap
What a breath-test result can—and cannot—tell you
- Alcohol tests: measure ethanol in breath under a specified procedure. They do not test for other drugs or diagnose disease.
- Clinical breath tests: measure a particular gas or metabolic change after a defined protocol. Their result applies to the test’s intended clinical use, not to every illness.
- Personal alcohol testers: belong to the screening-device category, not the evidential or medical categories. No specific consumer model’s accuracy or performance is established here, so a personal reading should not be used as a guarantee that it is safe or lawful to drive.
- Forensic and clinical instruments: have different purposes, controls and approval contexts. A result should not be generalized beyond the test and protocol that produced it.
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