A blood test checks for the presence of H. pylori antibodies, not for the bacteria itself. The biggest disadvantage of this test is quite simply;
Blood Tests cannot differentiate between a past infection and the current status of an H. pylori infection.
Even after H. pylori bacteria have been treated, H. pylori antibodies may sometimes still be present in the blood for 12 – 18 months after a successful treatment. This means that you will test positive (for antibodies) when you are actually negative after receiving treatment. In view of this, Blood Testing is considered to be the most inconclusive test that can be used to determine if a treatment has been successful or not.
If you have NEVER been treated for H. pylori a Blood test CAN be useful! If you suspect you are infected with H. pylori, and if you have never been treated for H. pylori before, and you test positive with a Blood Test – then you are extremely likely to be infected with H. pylori. Obviously, this means that you will need to start seeking effective treatment.