It's the ultimate noninvasive medical test: A growing number of health problems can be diagnosed by analyzing a patient's breath alone.

The concept goes back to Hippocrates, who wrote a treatise on breath aroma and disease around 400 B.C. For centuries afterward, doctors noticed that patients with liver and kidney disorders had distinctive smells to their breath.

Now, scientists are identifying thousands of chemical compounds that create those telltale odors. Tools called mass spectrometers can detect them in quantities as minute as parts per trillion, the equivalent of finding a single ping-pong ball in a thousand baseball fields filled with ping-pong balls.

And researchers are developing tests that can diagnose and monitor not just liver and kidney disorders, but also asthma, diabetes, tuberculosis, gastrointestinal infections