Ehrlichiosis: Laboratory Diagnosis

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The page below is a sample from the LabCE course Tickborne Diseases. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Ehrlichiosis: Laboratory Diagnosis

Nonspecific laboratory findings include leukopenia, thrombocytopenia, and elevated liver enzymes. Direct staining of peripheral blood or buffy coats with Wright or Giemsa stain may yield morulae (a cluster of organisms seen inside a white blood cell on a Wright- or Giemsa-stained smear of peripheral blood) but is only 20-29% sensitive. Polymerase chain reaction (PCR) of whole blood is the most frequently used method of diagnosis. Immunofluorescence antibody (IFA) is sensitive and specific when a four-fold rise in titer occurs but has the same limitations as those described in RMSF. IFA is not clinically useful due to the delay because it is negative in the first 7-10 days. It is usually positive in week three, with a peak titer at week six. Some tests may demonstrate a cross-reaction with Ehrlichia ewingii. Immunohistochemical (IHC) staining and cell culture can also yield a diagnosis.
22. Diagnosis and Management of Tickborne Rickettsial Diseases. Centers for Disease Control and Prevention, 13 May 2016, https://www.cdc.gov/mmwr/volumes/65/rr/pdfs/rr6502.pdf.

Intramonocytic morula associated with Ehrlichia chaffeensis infection (22).