Antibiotics don’t work against viruses. But doctors sometimes give antibiotics to patients who have what turns out to be a viral infection. Which adds to the growing problem of antibiotic resistance. Tests to tell a bacterial infection from a viral one take one to two days and don’t always return a clear prognosis. So researchers in Israel have developed a rapid test – using a CSI tool.

The chemical Luminol is used at crime scenes because it fluoresces in the presence of blood. When we get an infection, white blood cells called phagocytes leap into action. In the process, they consume oxygen and produce what are called Reactive Oxygen Species, or ROS. Luminol makes the ROS glow.

But bacterial and viral infections produce different ROS’s and so have different types of glows. By evaluating the infections of 69 patients, the researchers were able to create different Luminol signatures for bacterial versus viral infections. In blind tests, the scientists achieved 89 percent accuracy. The research was published in the journal Analytical Chemistry.

The scientists hope to fine-tune the test to make it more accurate. Which could help doctors make better diagnoses—and reduce the use of unnecessary antibiotics.