InstalabBartonella Antibodies
Should you take a Bartonella Antibodies test?
This test is most useful if any of these apply to you.
4 biomarkers included
- B. Henselae Antibody IgG ScreenDetects the longer-lasting antibody against the cat-associated species behind most cat scratch disease. It signals exposure or infection and, at very high levels, supports a heart valve infection.Why it mattersA high or rising level points to infection with the cat-linked species; a very high level supports Bartonella endocarditis.
- B. Henselae Antibody IgM ScreenDetects the early antibody against the cat-associated species, which rises soon after infection and fades within about 100 days.Why it mattersA positive result suggests a recent cat scratch-type infection, though this early antibody is often absent even in true cases.
- B. Quintana Antibody IgG ScreenDetects the longer-lasting antibody against the louse-associated species tied to trench fever and a large share of Bartonella heart valve infections.Why it mattersA strong result flags the louse-linked species, often the leading cause of Bartonella endocarditis.
- B. Quintana Antibody IgM ScreenDetects the early antibody against the louse-associated species, adding a timing clue for a recent trench fever-type infection.Why it mattersA positive result suggests recent infection with the louse-linked species; uncommon, but meaningful when it appears.
About Bartonella Antibodies
Some infections do not show up where you would expect. Bartonella bacteria hide inside the cells that line your blood vessels, so they rarely grow in a standard blood culture. They can quietly drive fevers, swollen glands, or a slow-burning heart valve infection for months without a clear cause.
This panel looks for your immune response instead of the bacteria themselves. It measures antibodies against the two Bartonella species that infect people most often, and reading all four results together, alongside a clinician's judgment, is what separates a recent infection from an old one.
What This Panel Reveals
The panel answers one question from two angles: which Bartonella species your body has reacted to, and how recently. One species, B. henselae, is the classic cause of cat scratch disease, usually spread by cat scratches, bites, or cat fleas. The other, B. quintana, spreads through body lice, causes trench fever, and accounts for a large share of Bartonella heart valve infections, though the exact proportion varies by region. Testing both widens the net so an infection is less likely to slip through.
Timing comes from two kinds of antibodies. The early kind (called IgM) rises first and usually fades within about 100 days, so it points toward a recent infection. The longer-lasting kind (called IgG) appears later and can linger for months to years, so it can mean either an active infection or one that resolved long ago.
One honest limit shapes how you read everything here. The two species share so much that their antibodies cross-react extensively. A positive result rarely tells you for certain which species you carry, which is why the panel is best treated as a supportive screen, read together with a clinician, rather than a final answer.
How to Read Your Results Together
No single number decides this. The pattern across the four results, read alongside your symptoms, is what carries meaning.
| What Your Results Show | What It Often Points To |
|---|---|
| Early antibody (IgM) positive, long-lasting antibody (IgG) low or negative | A possible recent infection, though this pattern is uncommon and can be a false alarm |
| Long-lasting antibody (IgG) positive, early antibody (IgM) negative | Past exposure or a longer-standing infection rather than a brand-new one |
| High IgG to one or both species, with fever or heart symptoms | Stronger support for active infection, including a heart valve infection worth prompt follow-up |
| All four negative | Bartonella is less likely, but a negative result does not fully rule it out |
Titer height matters most for heart valve infection. In one series of confirmed Bartonella endocarditis cases, an IgG level at or above 1:800 was found in 94% of patients, which is why that threshold is treated as strong support and is now part of the 2023 Duke-ISCVID diagnostic criteria. Cutoffs differ by laboratory, though: using a commercial test at a lower 1:256 threshold, another endocarditis cohort found IgG positive in 96.7% of patients with available blood. Ask which cutoff your lab uses before comparing your number to any single rule.
What to Do with Your Results
A high IgG paired with fevers, night sweats, weight loss, or a known heart murmur is a reason to move quickly. The next steps are an echocardiogram to look at the valves and a DNA-based test (called PCR) run on blood or, when surgery happens, on valve tissue. PCR on tissue is the most definitive confirmation and can also name the exact species that serology cannot.
A negative or low-level result does not close the door. The early antibody test can miss true infections, with one commercial IgM assay showing a sensitivity of only 6%, and low IgG readings are easy to overread. Among children tested for cat scratch disease, one-third of those with a 1:128 titer turned out to have a different diagnosis. If your immune system is deeply suppressed, such as in advanced HIV, antibodies may never rise; up to a quarter of culture-positive patients with advanced HIV never develop them, so PCR is the better path when suspicion stays high.
Serial testing sharpens the picture. If a first sample is drawn early, a repeat drawn a few weeks later can catch a fourfold rise in antibody level, which is the clearest signal of a recent infection. Because tick and flea exposures often overlap, adding tests for Lyme and other tick-borne infections can round out the workup when the cause of your symptoms is still unclear.
When Results Can Be Misleading
A few things move several results at once. Antibodies to Bartonella can cross-react with the bacteria behind Q fever and with Chlamydia, so a positive Bartonella result sometimes reflects a different infection entirely. Background exposure is common too: in healthy comparison groups, 9% to 18% carried Bartonella IgG without illness. And very early in an infection, before your body has built antibodies, the whole panel can read negative even when the bacteria are present.