Bartonella henselae IgG checks your blood for IgG antibodies against B. henselae, the bacterium most often responsible for cat-scratch disease (CSD). IgG usually reflects past exposure; rising or very high IgG levels can also be seen during active infection. Labs typically use an IFA (indirect immunofluorescence assay) and report results as titers (e.g., 1:64, 1:128, 1:256). Exact cutoffs vary by lab.
When is the Bartonella henselae IgG test is ordered
Your clinician may order Bartonella IgG if you have symptoms compatible with cat-scratch disease (tender, enlarged lymph nodes after a cat scratch or bite), if you have certain eye problems (like neuroretinitis), culture-negative endocarditis, or if you’re immunocompromised. CSD often starts with a small bump or blister at the scratch site, then lymph nodes swell 1–3 weeks later.
What the test can and can’t tell you
Can:
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Support a diagnosis of Bartonella infection when your history and exam fit.
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Show prior exposure or, with paired tests, show a rising titer consistent with a recent infection.
Can’t:
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Pinpoint timing of infection from a single positive result (IgG may persist long after you feel better).
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Identify the exact Bartonella species (there’s cross-reactivity among species).
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Rule out disease in every case—some patients with typical CSD can have negative or low antibodies early on. CDC+1
IgG vs IgM vs PCR—what’s the difference?
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IgG: Rises weeks after exposure; may remain detectable long-term. Helpful for past exposure and, with paired testing, for recent infection.
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IgM: More suggestive of recent/acute infection when positive, but may be transient and is not always detected.
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PCR (molecular testing): Looks for bacterial DNA in a sample (e.g., lymph node aspirate). Useful in select cases, but blood PCR has limited sensitivity, and lymph node aspiration is not routinely done unless diagnosis is unclear or to relieve significant pain.
Typical symptoms & course (why your doctor ordered this)
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Small bump/papule at the scratch or bite, often 3–10 days after exposure.
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Tender, enlarged lymph nodes near the area 1–3 weeks later; fever and fatigue are common.
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Most immunocompetent people recover without complications; special forms (eye disease, liver/spleen involvement, endocarditis) need targeted care.
Common reasons results seem confusing
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Different lab cutoffs. One lab’s “positive” may be another’s “equivocal.” Always use your report’s ranges.
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Past exposure. IgG can stay positive for years, even after successful treatment, so context matters.
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Cross-reactivity. Antibodies may react with other Bartonella species; serology doesn’t cleanly distinguish them.
What to do next
If your IgG is negative but you have classic symptoms:
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Talk to your clinician about retesting in a couple of weeks or adding IgM and/or PCR (especially if diagnosis is uncertain).
If your IgG is equivocal:
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Plan a repeat IgG in 10–14 days to look for a rising titer. Your provider may add IgM or other tests.
If your IgG is positive:
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Discuss your symptoms and timing with your clinician. A single positive may reflect past exposure; paired testing or clinical findings help determine if it’s active.
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Treatment decisions depend on your situation (symptom severity, immune status, location of disease). Many uncomplicated cases in healthy people improve without complications; antibiotics are sometimes used—your clinician will advise. NCBI
If you’re immunocompromised (e.g., advanced HIV, chemotherapy):
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Seek care promptly—bartonellosis can be more severe and may require specific antibiotic therapy and closer follow-up.
Reducing your risk (cat-related practical tips)
You do not need to test or treat a healthy cat. Lower risk by keeping cats indoors when possible, avoiding scratches/bites, washing any scratches promptly, and using flea control for pets.
Key takeaways
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Bartonella henselae IgG helps show prior exposure and, with paired tests, may support recent infection.
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A single positive doesn’t prove active disease; clinical context is essential.
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Equivocal results usually call for repeat testing.
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When needed, IgM and PCR can add information, but each has limits.
Bartonella henselae IgG
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