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Ehrlichia monocytic morula/CDC

Ehrlichiosis: Laboratory Diagnosis

Nonspecific laboratory findings include leukopenia, thrombocytopenia, and elevated liver enzymes. Direct staining of peripheral blood or buffy coats with Giemsa or Wright 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 3 with a peak titer at week 6. Some tests may demonstrate a cross reaction with Erhlichia ewingii. Immunohistochemical (IHC) staining and cell culture can also yield a diagnosis.