There are currently four ways to diagnose H. pylori infection. During endoscopy (a visual exam of the stomach through a thin, lighted, flexible tube), the physician can remove small bits of tissue through the tube. The tissue is then tested for the bacteria. A breath test is also available. In this test a substance called urea is given by mouth. A strong enzyme in the bacteria breaks down the urea into carbon dioxide, which is then exhaled and can be measured. There is a blood test that measures the protein antibodies against these bacteria that are present in the blood. The blood is generally not useful in detecting acute disease and mostly represents a past exposure to the bug. This antibody can mean the infection is present, or that it was present in the past. Finally, there is fecal antigen test that is very accurate and inexpensive.