What are Breath Tests?

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  • Written By: Donn Saylor
  • Edited By: John Allen
  • Last Modified Date: 11 October 2019
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Breath tests are medical testing procedures that gauge and diagnose illness by analyzing air expelled from the lungs. There are several common types of breath tests, including breathalyzers, exhaled nitric oxide tests, hydrogen breath tests, and urea breath tests. With each of these procedures, the breath a patient emits during exhalation is examined utilizing special diagnostic tools, allowing various ailments — including asthma, dietary illnesses, and peptic ulcer disease — to be monitored and identified.

The ancient Greek physician Hippocrates was one of the first scholars to recognize the relationship between breath and health. Hippocrates deduced that bad breath could be indicative of disease. This pioneering idea laid the groundwork for the studies of breath that took place over the next several centuries, reaching their zenith in the 1970s. It was then that Linus Pauling, a Nobel Prize-winning chemist, found 250 chemicals in human breath. Since then, research has continued, and nearly 1000 chemicals have been successfully identified.

It is these chemicals that are analyzed during a breath test. A patient breathes into the testing unit, typically via a small tube, and the breath sample is collected and sent for examination. Many breath tests are administered in a very short period of time — about 5–15 minutes apart — and are noninvasive procedures.


A breathalyzer is the most widely known type of breath test. These machines determine an individual's blood alcohol content through analysis of the breath. Breathalyzers are commonly used by law enforcement to curb drunk driving, though they are also sold for at-home use.

In exhaled nitric oxide tests, breath tests are often administered to determine the level of exhaled nitric oxide (eNO) in the blood. It has been established that eNO levels are elevated in individuals with asthma. The eNO test can provide valuable information toward making a definitive medical diagnosis of asthma. Other illnesses that can be identified by an eNO test include airway inflammation and other respiration problems.

Hydrogen breath tests are used to determine deficiencies in diet and diagnose diet-related illnesses. The most common ailments identified by this testing method are lactose intolerance, fructose intolerance and malabsorption, and small intestinal bacterial overgrowth syndrome. These findings are deduced by studying the levels of hydrogen, methane, and other gasses in the breath.

Breath tests known as urea breath tests can detect Helicobacter pylori (H. pylori) organisms, which set in motion a process that can lead to the denigration of the stomach lining, or peptic ulcers. The test reads carbon dioxide levels in the body, which help identify the presence of H. pylori. H. pylori is a serious medical concern and leads to a half a million new stomach cancer diagnoses each year.


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