Ehrlichiosis Workup

Updated: Jun 22, 2021
  • Author: Chinelo N Animalu, MD, MPH, 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.


Diagnostic Workup

The diagnosis of human monocytic ehrlichiosis (HME) or human granulocytic anaplasmosis (HGA) rests on several testing methods:

Serology (2 types): (1) indirect fluorescent antibody and (2) enzyme-linked immunosorbent assays.

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]

Buffy coat examination: 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.

Polymerase chain reaction: Detection of the organism with polymerase chain reaction (PCR) assay is now becoing widely available. Sensitivity and specificity of assays may vary but has been reported as high as 95-100 percent by some laboratories. [15]

Immunohistochemical stains: Although not a preferred method, immunohistochemical stains have been used to make the diagnosis of ehrlichiosis and anaplasmosis in a few patients through bone marrow staining tissue or autopsy tissue such as spleen, lymph nodes, liver, or lung. [16]   

Culture: The infecting organism is extremely difficult to culture from blood and therefore is not recommended.



Laboratory Studies

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.