The IgG Ehrlichia test measures antibodies against Ehrlichia species, bacteria transmitted by ticks that cause ehrlichiosis, a potentially serious tick-borne illness. The two main human pathogens are Ehrlichia chaffeensis (human monocytic ehrlichiosis, HME) and Ehrlichia ewingii. Infections can lead to fever, chills, muscle aches, headache, and sometimes severe complications if untreated.
What IgG Ehrlichia Means
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IgG antibodies typically develop within 2–4 weeks after infection and may remain present for months or years.
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A positive IgG result usually indicates past exposure or immune memory to Ehrlichia.
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Since IgM antibodies reflect more recent infection, IgG testing is most useful for assessing later or past stages of ehrlichiosis.
Clinical Importance
Testing for IgG Ehrlichia can be important in patients with:
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Unexplained fever, fatigue, headache, or muscle pain following a tick bite
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Low white blood cell counts, low platelets, or abnormal liver tests often seen in ehrlichiosis
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Persistent or relapsing symptoms after tick exposure in endemic regions
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Suspected co-infections with other tick-borne pathogens such as Borrelia (Lyme disease) or Babesia
Patient Takeaway
A positive IgG Ehrlichia result means your immune system has recognized the bacteria at some point, suggesting prior exposure or infection. This does not always mean the infection is currently active, since IgG antibodies may persist long-term.
Your healthcare provider will interpret this result together with your symptoms, tick exposure history, and other test results (including IgM, PCR, or blood smear) to determine whether ehrlichiosis is active or past.
If your result is reported as equivocal (borderline), antibody levels are close to the cutoff and not clearly positive or negative. In these cases, repeat or confirmatory testing is often recommended.
IgG Ehrlichia
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