Bacterial infection of the blood can result in a condition called sepsis, the most common cause of death in intensive care units. This type of infection can lead the body to make chemicals that cause a severe form of inflammation, called the systemic inflammatory response syndrome (SIRS). This syndrome occurs in patients with sepsis and in sick people who do not have sepsis. Telling the difference between SIRS with sepsis and SIRS with no sepsis is important because patients with sepsis need immediate treatment with antibiotics. It can be very difficult to know if a patient with SIRS also has sepsis, so a test for sepsis would be helpful. Doctors do test for bacteria in the blood, but this test can take many hours to become positive. The ideal test would give an answer right away, so that doctors could decide whether to use antibiotics and be fairly sure they made the right decision. Doctors usually start antibiotics immediately when they suspect sepsis, so many patients who don't have sepsis get antibiotics for several days until results of blood tests for bacteria are negative. Exposure to antibiotics can be harmful.