The Ehrlichia immuno-fluorescence assays (IFAs), Anaplasma phagocytophilum IFA (HGA IFA) and Ehrlichia chaffeensis IFA (HME IFA) are designed to detect human IgG and IgM antibodies to HGA and HME antigens respectively in human serum. For diagnostic purposes, HGA and HME IFA test results should be used in conjunction with other information available to the physician.


The Ehrlichia IFA assay is a “two-stage” sandwich assay, based upon an antigen-antibody complex formation in the following steps:

  1. Binding of anti-Ehrlichia specific antibodies in human serum to fixed Ehrlichia
  2. Binding of fluorescent-labeled anti-human IgG/IgM antibodies to the human anti– Ehrlichia antibodies bound to Ehrlichia on the slide. 
  3. Identifing  green fluorescing Ehrlichia organisms  with a fluorescent microscope.x. 

Note: For HGA IFA, A. phagocytophilum is fixed to the slide and for HME IFA, Ehrlichia chaffeensis is fixed on the slide.

Result Interpretation

Reference Range

  • HME or HGA antibody titers IgM        <20
  • HME or HGA  antibody titers IgG        <40

Clinical Significance

The Ehrlichia chaffeensis (HME) immunofluorescent antibody test is used to detect antibodies to Ehrlichia chaffeensis in human serum. The Anaplasma phagocytophilum (HGA) immunofluorescent antibody test is used to detect antibodies to Anaplasma phagocytophilum in human serum. Titers rise during the first 2 to 4 weeks of illness and decline over 6 to 12 months. In patients with previously high titers, presence of only IgG titer of <160 may indicate a resolving infection. If the IFA result is negative but the clinical symptoms of HME or HGA infection are present PCR testing is suggested. E. chaffeensis  and  A. phagocytophilum are carried by the same ticks that have also been known to cause babesiosis, bartonellosis and Lyme disease. Patients with positive titers should also be tested for other tick-borne diseases.


  1. A negative HME IFA test result does not exclude the possibility of E. chaffeensis infection.
  2. A negative HGA IFA test result does not exclude the possibility of A. phagocytophilum infection.
  3. Cross-reactions can occur among the Rickettsiaceae, including: Rickettsia, Ehrlichia and Anaplasma.
  4. Results should be interpreted in conjunction with other laboratory and clinical findings.

Ordering Information

  • Specimen: Serum - minimum volume 0.5 ml
  • Container: SST (Serum Separator Tube) OR Leak-proof tube
  • Collection and Shipping Instructions: See Serum and Whole Blood Samples- Collection & Shipping Instructions [THIS WILL LINK TO THAT PAGE]

Tests Offered

Test# 203 HME (Monocytic) IgG & IgM Antibody CPT Code 86666 x2
Test# 206 HGA (Anaplasma phagocytophilum) IgG & IgM Antibody CPT Code 86666 x2
HME (Monocytic) IgG & IgM Antibody and HGA (Anaplasma phagocytophilum) IgG & IgM Antibody is part of the following Test Panels:
Test Panel# 5080 Western Regional Co-infection Panel**
Test Panel# 5085 New Western Regional Co-infection Panel**(includes Bartonella FISH)
Test Panel# 5090 Complete Co-infection Panel
Test Panel# 5095 New Complete Co-infection Panel(includes Bartonella FISH)
Test Panel# 5060 TBD Panel**
Test Panel# 2020 Complete Ehrlichia Panel

**Test/Panels are not yet available for New York Residents