Can you tell how long you've had h.Pylori by your blood test?

No. You cannot tell how long you've had it. Many people are carriers and have no active disease being caused by h. Pylori. Biopsy is one of the ways for diagnosis. There is an h. Pylori breath test, a stool antigen test, and blood tests for antibodies to h. Pylori. These test won't really capture how long you've had it. And frankly, its not altogether important in DX and tx.
Nope. Levels on the blood test give us no clue about how long you've had it. When we treat you, our medical regimens are only about 80 % effective, and you should have a stool test for h pylori several months after treatment to ensure that it is gone.
Not exactly. Presence of antibodies to the h pylori tells you that you have or have had infection, but not how long.
No. You can test for the presence of the h. Pylori, or if you have antibodies to it, but not the length of time you have been carrying it.
Usually not. The long answer is that it depends on the test. You can check igg, iga, or IgM antibodies for h pylori. Some specify short term recent infection, others long. Most doctors usually don't check all three, which is appropriate. Bottom line, duration usually doesn't matter.