Test Catalog

Test ID: EHRC    
Ehrlichia chaffeensis (HME) Antibody, IgG, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

As an adjunct in the diagnosis of ehrlichiosis

 

Seroepidemiological surveys of the prevalence of the infection in certain populations

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Ehrlichia chaffeensis is an intracellular rickettsia-like bacterium that preferentially infects monocytes and is sequestered in parasitophorous vacuoles referred to as morulae. Infections with E chaffeensis are also referred to as human monocytotropic ehrlichiosis (HME). E chaffeensis is transmitted by Amblyomma species ticks, which are found throughout the southeastern and south central United States.

 

Many cases of HME are subclinical or mild, however, the infection can be severe and life-threatening, particularly in immunosuppressed individuals. Reported mortality rates range from 2% to 3%. Fever, fatigue, malaise, headache, and other "flu-like" symptoms occur most commonly. Leukopenia, thrombocytopenia, and elevated hepatic transaminases are frequent laboratory findings.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

<1:64

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

A positive immunofluorescence assay (titer > or =1:64) suggests current or previous infection. In general, the higher the titer, the more likely the patient has an active infection. Four-fold rises in titer also indicate active infection.

 

Previous episodes of ehrlichiosis may produce a positive serology although antibody levels decline significantly during the year following infection.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Serology for IgG may be negative during the acute phase of infection (<7 days postsymptom onset), during which time detection using targeted nucleic acid amplification testing (eg, PCR) is recommended.

 

Detectable IgG-class antibodies typically appear within 7 to 10 days postsymptom onset.

 

IgG-class antibodies may remain detectable for months to years following prior infection. Therefore, a single time point-positive titer needs to be interpreted alongside other findings to differentiate recent versus past infection.

 

Other members of the Ehrlichia genus (eg, E ewingii) may not be detected by this assay.

Clinical Reference Recommendations for in-depth reading of a clinical nature

CDC. Tick-borne diseases of the United States: A Reference Manual for Health Care Providers. Fourth Edition, 2017

Special Instructions Library of PDFs including pertinent information and forms related to the test