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Test Code EHRC Ehrlichia chaffeensis (HME) Antibody, IgG, Serum

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

Ehrlichia Chaffeensis (HME) Ab, IgG

Specimen Type

Serum


Specimen Required


Container/Tube: 

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL


Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross reject

Icterus

NA

Other

Heat-inactivated specimen

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 14 days
  Frozen  14 days

Specimen Minimum Volume

0.15 mL

Day(s) and Time(s) Performed

Monday through Friday; 9 a.m.

Specimen Retention Time

14 days

Analytic Time

Same day/1 day

Reference Values

<1:64

Useful For

As an adjunct in the diagnosis of ehrlichiosis and/or in seroepidemiological surveys of the prevalence of the infection in certain populations

 

Ehrlichiosis is sometimes diagnosed by observing the organisms in infected WBCs on Giemsa-stained thin blood films of smeared peripheral blood (morulae). Serology may be useful if the morulae are not seen or if the infection has cleared naturally or following treatment.

 

Serology may also be useful in the follow-up of documented cases of ehrlichiosis or when coinfection with other tick- transmitted organisms is suspected. In selected cases, documentation of infection may be attempted by PCR methods.

Method Name

Immunofluorescence Assay (IFA)

Test Classification

This test was developed using an analyte specific reagent. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

86666

LOINC Code Information

Test ID Test Order Name Order LOINC Value
EHRC Ehrlichia Chaffeensis (HME) Ab, IgG 47405-6

 

Result ID Test Result Name Result LOINC Value
81478 Ehrlichia Chaffeensis (HME) Ab, IgG 47405-6

Clinical Information

Ehrlichiosis is an emerging zoonotic infection caused by obligate intracellular, gram-negative rickettsia that infect leukocytes.

 

Human monocytic ehrlichiosis (HME) is caused by Ehrlichia chaffeensis and is transmitted by the Lone Star tick, Amblyomma americanum. The deer is believed to be the animal reservoir and most cases of HME have been reported from the southeastern and south-central region of the United States.

 

Infectious forms are injected during tick bites and the organism enters the vascular system where it infects monocytes. It is sequestered in host-cell membrane-limited parasitophorous vacuoles known as morulae. These can be readily observed on Giemsa- or Wright-stained smears of peripheral blood from infected persons. Macrophages in organs of the reticuloendothelial system are also infected. Asexual reproduction occurs in WBCs and daughter cells are formed which are liberated upon cell rupture.

 

Most cases of ehrlichiosis are probably subclinical or mild, but the infection can be severe and life-threatening; there is a 2% to 3% mortality rate. Fever, fatigue, malaise, headache, and other "flu-like" symptoms occur most commonly. Central nervous system involvement can result in seizures and coma. Leukopenia, thrombocytopenia, and elevated hepatic transaminases are frequent laboratory findings.

Interpretation

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

Cautions

Serology for IgG may be negative during the acute phase of infection but a diagnostic titer usually appears by the third week after onset. Previous episodes of ehrlichiosis may produce a positive serology although antibody levels decline significantly during the year following infection.

 

Performance characteristics have not been established for hemolyzed or lipemic specimens.

Clinical Reference

Fishbein DB, Dawson JE, Robinson LE: Human ehrlichiosis in the United States, 1985 to 1990. Ann Intern Med 1994;120:736-743

Method Description

Immunofluorescence assay technique using antigen substrate slides consisting of a cell culture infected with Ehrlichia chaffeenis.(Dawson JE, Fishbein DB, Eng TR, et al: Diagnosis of human ehrlichiosis with the indirect fluorescent antibody test: kinetics and specificity. J Infect Dis 1990;162:91-95)