BREATH TEST: A woman breathes into a collection tube for two minutes, providing a breath sample that could potentially be used to screen for a variety of diseases
COURTESY OF MENSSANA RESEARCH, INC.

Most of us associate Breathalyzers with drunk-driving arrests. But breath tests can reveal a lot more than how many alcoholic beverages a person chugged. They're also used to diagnose some medical conditions, including jaundice in babies, lactose intolerance and ulcers, as well as to monitor whether asthma drugs are effective. And researchers say breath analyzers may one day be used to quickly identify a slew of other disorders, including cancer, leading to early detection and treatment.

The way these tests work: Every time you take a breath, you inhale oxygen and exhale carbon dioxide (CO2), along with at least a thousand other chemicals that actually provide a so-called "breathprint," or unique breath profile of your health. The first person to recognize—or at least write about—this phenom was Hippocrates (460 B.C. to 377 B.C.), considered to be the father of medicine, who suggested that bad breath was a sign of disease. But it was not until late last century that scientists actually identified many of these chemicals.

In 1971, researchers led by Nobel Prize winning chemist Linus Pauling identified about 250 breath chemicals using gas–liquid partition chromatography (which  separates molecules based on their boiling points and polarity, or unequal electrical charges).

Thanks to improvements in laboratory techniques, scientists have since identified at least 1,000 different chemicals in human breath, a few of which have become the basis of medical tests. The U.S. Food and Drug Administration (FDA) has approved six medical breath tests, according to Terence Risby, a professor of environmental health science at Johns Hopkins Bloomberg School of Public Health in Baltimore.

The most common is one used to determine whether breathing tubes are correctly positioned in patients' lungs (occasionally doctors accidentally thread the tube through the esophagus and into the stomach), according to Raed Dweik, a pulmonologist and director of the Pulmonary Vascular Program at the Cleveland Clinic in Ohio. If the tube is properly placed, CO2 moves from the lungs and out through the tube; if not, carbon dioxide will not flow out. A golf ball-size CO2 detector changes color when it picks up the gas, signaling to doctors that the tube is positioned correctly. Another type of carbon dioxide detector known as a capnograph is routinely used in hospitals to continuously monitor the amount of CO2 exhaled by patients anesthetized for surgery or hooked up to ventilators to help them breath. Dweik says that doctors can determine if patients are getting enough oxygen by the amount of carbon dioxide leaving their bodies. 

Physicians now also use a breath test to determine whether asthma meds are working by measuring the amount of nitric oxide a patient with the respiratory illness exhales. According to Dweik, people with asthma, which is marked by chronic inflammation of the airways and difficulty breathing, exhale abnormally high levels of nitric oxide, a gas  that regulates blood flow but may damage cells and cause inflammation if overproduced in the airways: The nitric oxide content of an asthmatic's breath can be as high as 100 or 200 parts per billion or ppb (100 nitric oxide molecules in every billion exhaled molecules) compared with the 10 to 20 ppb in each breath of a nonasthmatic person.

If an asthma patient is not exhaling normal nitric oxide levels within days of beginning a treatment, it indicates the therapy is not effective and another one should be tried. "The whole test takes about five minutes," Dweik says, noting that a patient breathes into a tube attached to a breath analyzer, which produces an electronic readout of nitric oxide concentrations.

Physicians can diagnose lactose intolerance with a test that identifies abnormally high levels of hydrogen in the breath produced by gut bacteria that gobble lactose when the body fails to break down the milk sugar on its own. In addition, jaundice in babies can be confirmed with a test that scans the breath for high levels of carbon monoxide produced when the liver is not functioning properly, and there's a breath test that identifies the presence of the ulcer-promoting intestinal bacteria Helicobacter pylori (H. pylori).