A negative blood test for H. pylori is normal. H. pylori serological test, serological test by indirect enzyme-linked immunosorbent assay, when the test result is positive, it indicates the presence of H. pylori infection. The H. pylori serology test is only negative and positive and is not a specific value. Patients who test positive can further do a carbon 13 or carbon 14 breath test, which indicates H. pylori infection if the carbon 13 test is greater than 4 or the carbon 14 test is greater than 100. H. pylori is a bacterium that can invade the body and survive in the digestive tract, causing ulcers in the human stomach and upper small intestine after years of multiplication in the body. For some patients, the infection may cause gastric cancer, so once the H. pylori infection is diagnosed, early treatment should be given to avoid aggravation of the disease.