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Test ID: BABG Babesia microti IgG Antibodies, Serum

Reporting Name

Babesia microti IgG Ab, S

Useful For

An adjunct in the diagnosis of babesiosis


Follow-up of documented babesiosis

Clinical Information

Babesiosis is a zoonotic infection caused by the protozoan parasite Babesia microti. The infection is acquired by contact with Ixodes ticks carrying the parasite. The deer mouse is the animal reservoir, and overall, the epidemiology of this infection is much like that of Lyme disease. Babesiosis is most prevalent in the Northeast, upper Midwest, and Pacific Coast of the United States.


Infectious forms (sporozoites) are injected during tick bites, and the organism enters the vascular system where it infects red blood cells (RBC). During this intraerythrocytic stage, it becomes disseminated throughout the reticuloendothelial system. Asexual reproduction occurs in RBC, and daughter cells (merozoites) are formed that are liberated on rupture (hemolysis) of the RBC.


Most cases of babesiosis are subclinical or mild, but the infection can be severe and life-threatening, especially in older or asplenic patients. Fever, fatigue, malaise, headache, and other flu-like symptoms occur most commonly. In the most severe cases, hemolysis, acute respiratory distress syndrome, and shock may develop. Patients may have hepatomegaly and splenomegaly.


A serologic test can be used as an adjunct in the diagnosis and follow-up of babesiosis, when infection is chronic or persistent, or in seroepidemiologic surveys of the prevalence of the infection in certain populations. Babesiosis is usually diagnosed by observing the organisms in infected RBC on Giemsa-stained thin blood films of smeared peripheral blood. Serology may also be useful if the parasitemia is too low to detect or if the infection has cleared naturally or following treatment.


A positive result of an indirect fluorescent antibody test (titer ≥1:64) suggests current or previous infection with Babesia microti. In general, the higher the titer, the more likely it is that the patient has an active infection. Patients with documented infections have usually had titers ranging from 1:320 to 1:2560.

Testing Algorithm

For more information see Acute Tick-Borne Disease Testing Algorithm.

Report Available

Same day/1 to 3 days

Day(s) Performed

Monday through Friday

Clinical Reference

1. Spach DH, Liles WC, Campbell GL, Quick RE, Anderson Jr DE, Fritsche TR: Tick-borne diseases in the United States. N Engl J Med. 1993 Sep 23;329(13):936-947

2. Vannier E, Gelfand JA: Babesia species. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Elsevier; 2020:3400-3409

Method Name

Immunofluorescence Assay (IFA)

Specimen Type


Specimen Required

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.

Specimen Minimum Volume

0.4 mL

Specimen Stability Information

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

Reference Values


Reference values apply to all ages.

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 US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
BABG Babesia microti IgG Ab, S 16117-4


Result ID Test Result Name Result LOINC Value
81128 Babesia microti IgG Ab, S 16117-4


If not ordering electronically, complete, print, and send Infectious Disease Serology Test Request (T916) with the specimen.

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-CNS-Infections, mml-Pediatric