Bartonella are a group of bacteria spread primarily through cats, fleas, or ticks. The most well-known infection is cat scratch disease, which can cause fever, swollen lymph nodes, and fatigue. In some cases, especially in people with weakened immune systems, Bartonella can lead to more serious problems such as infections of the heart, eyes, or nervous system.
When the body encounters Bartonella, it produces antibodies, specialized proteins made by the immune system. Two types are typically measured: IgM and IgG. IgM antibodies usually appear first, within a few days to weeks of infection, and suggest a more recent or active infection. IgG antibodies develop later and can persist for months or years, indicating past exposure. Interpreting the test depends on the pattern: high IgM often signals a recent infection, while IgG alone may mean a prior infection or immunity.
That said, antibody tests are not perfect. Some people may carry Bartonella without symptoms, while others may test negative early in infection before antibodies develop. Cross-reactivity with other bacteria can sometimes cause false positives. Doctors often interpret results alongside symptoms, history of exposure, and sometimes additional tests such as blood cultures or PCR.
