Ehrlichiosis laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.

Overview

There are three primary laboratory methods to diagnose an ehrlichiosis infection, polymerase chain reaction (PCR), peripheral blood smear, and an immunofluorescence assay (IFA). Polymerase chain reaction and peripheral blood smear exams are most effective when conducted early on in the diagnoses. The gold standard serologic test for ehrlichiosis is the immunofluorescence assay. The test is most effective when conducted once early on in the infection and a second time, later in the infection. Infection rates will show in increase within an IFA as the illness progresses.

Laboratory Findings

Polymerase chain reaction (PCR)

• Most effective within the acute phase of illness (first week of illness).
• Negative result does not completely rule out analysis.

Peripheral Blood Smear

• Most effective during the first week of illness.
• May reveal morulae (microcolonies of ehrlichiae.)
• Identifying the type of infected blood cell may indicate the infecting species.
  • E. chaffeensis infects monocytes.
  • E. ewingii infects granulocytes.
• Verification of infecting species must be confirmed with a culture isolation at a specialized laboratory.

Immunofluorescence assay

• Gold standard serologic test for ehrlichiosis.
• Sample should be extracted as early in the disease as possible.
• A second sample should be taken 2-4 weeks later.
• Typically the first count is low, however will significantly increase by the second sample.
• Testing should include both an IgM and IgG titer.