Test Catalog

Test ID: ANAP    
Anaplasma phagocytophilum (Human Granulocytic Ehrlichiosis) Antibody, Serum

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

As an adjunct in the diagnosis of human granulocytic 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.

See Acute Tick-Borne Disease Testing Algorithm in Special Instructions.

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

Anaplasma phagocytophilum, an intracellular rickettsia-like bacterium, preferentially infects granulocytes and forms inclusion bodies, referred to as morulae. A phagocytophilum is transmitted by Ixodes species ticks, which also transmit Borrelia burgdorferi and Babesia species. Infection with A phagocytophilum is also referred to as human granulocytic anaplasmosis (HGA) and symptoms in otherwise healthy individuals are often mild and nonspecific, including fever, myalgia, arthralgia, and nausea. Clues to the diagnosis of anaplasmosis in a patient with an acute febrile illness after tick exposure include laboratory findings of leukopenia or thrombocytopenia and elevated liver enzymes. HGA is most prevalent in the upper Midwest and in other areas of the United States that are endemic for Lyme disease.

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.


Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

A positive result of an immunofluorescence assay (IFA) test (titer > or =1:64) suggests current or previous infection with human granulocytic ehrlichiosis. In general, the higher the titer, the more likely it is that the patient has an active infection.


Seroconversion may also be demonstrated by a significant increase in IFA titers.


During the acute phase of the infection, serologic tests are often nonreactive, polymerase chain reaction (PCR) testing is available to aid in the diagnosis of these cases (see EHRL / Ehrlichia/Anaplasma, Molecular Detection, PCR, Blood).

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

Previous episodes of human granulocytic ehrlichiosis may produce a positive serologic result.


In rare instances, clinical evidence of infection may also be derived by direct microscopic examination of Giemsa- or Diff-Quik-stained peripheral blood buffy coat smears, which may reveal clusters of round, dark-purple stained, small dots or clusters of dots (morulae) in the cytoplasm of polymorphonuclear cells. However, this is a very insensitive method.


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

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

Center for Disease Control and Prevention (CDC): Tick-borne diseases of the United States: A Reference Manual for Health Care Providers. 5th ed. CDC; 2018

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