Ehrlichiosis SerologyHuman Granulocytic Anaplasmosis (HGA)Human Granulocytic Ehrlichiosis (HGE)Anaplasma phagocytophilum
Anaplasma phagocytophilum Ab, IgG, S (ANAP)
As an adjunct in the diagnosis of human granulocytic ehrlichiosis
Seroepidemiological surveys of the prevalence of the infection in certain populations
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.
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 apply to all ages.
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).