Ehrlichiosis Workup

Updated: Oct 15, 2018
  • Author: Walid Abuhammour, MD, MBA, FAAP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Approach Considerations

Lumbar puncture may be necessary in patients with fever and severe headache to rule out meningitis.

Buffy coat examination may reveal morulae, which are diagnostic characteristics of HME/HGA. Morulae are observed in the cytoplasm of neutrophils in patients with HGA and in monocytes in patients with HME. Only a minority of patients with HME have detectable morulae.


Lab Studies

The diagnosis of human monocytic ehrlichiosis (HME) or human granulocytic anaplasmosis (HGA) rests on (1) a single elevated immunoglobulin G (IgG) immunofluorescent antibody (IFA) Ehrlichia titer or (2) demonstration of a 4-fold or greater increase between acute and convalescent IFA Ehrlichia titers. [1]

Ehrlichiosis may also be diagnosed by demonstrating characteristic morulae in the cytoplasm of leukocytes. Morulae are diagnostic of ehrlichiosis and occur more frequently in HGA than in HME. The microbiology laboratory should be alerted to look carefully in the blood smear for them.

The infecting organism is extremely difficult to culture from blood. Detection of the organism with polymerase chain reaction (PCR) assay is possible. [11]

A complete blood cell (CBC) count should be obtained for possible neutropenia, relative lymphopenia, and/or thrombocytopenia. Anemia is not a feature of ehrlichiosis and, if present, is not a hemolytic anemia, as in babesiosis.

Atypical lymphocytes have been reported in patients with ehrlichiosis. The erythrocyte sedimentation rate (ESR) is minimally/moderately elevated in ehrlichiosis.

Elevated C-reactive protein (CRP) levels are common in the first week of illness and typically resolve by the end of the second week.

Serum transaminases are frequently mildly elevated in ehrlichiosis, as well as in other tick-borne infectious diseases. Abnormal liver enzymes are found in 86% of patients.

If other infectious diseases are suspected, appropriate tests should be obtained to rule out these diagnoses. If coinfection with RMSF or babesiosis is suspected, appropriate serology should be obtained to diagnose each of these infectious diseases.

Microscopic examination (by an experienced microbiologist) of blood smears stained with eosin-azure type dyes, such as Wright-Giemsa stain, may reveal morulae in the cytoplasm of leukocytes. As many as 20% of patients with HME and 20-80% of patients with HGA may have morulae in the first week of infection. A negative result should not be taken as proof of no infection.

Hyponatremia (< 130 mEq/L) is found in 40% of patients.