Test Catalog

Test ID: BABG    
Babesia microti IgG Antibodies, Serum

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

An adjunct in the diagnosis of babesiosis


Follow-up of documented babesiosis

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

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). In 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 probably 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.

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 indirect fluorescent antibody test (titer > or =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 1:2,560.

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

Previous episodes of babesiosis may produce a positive serologic result.


In selected cases, documentation of infection may be attempted by animal inoculation or polymerase chain reaction (PCR) methods (LBAB / Babesia species, Molecular Detection, PCR, Blood) 


Performance characteristics have not been established for the following specimen characteristics:



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

1. Spach DH, Liles WC, Campbell GL, et al: Tick-borne diseases in the United States. N Engl J Med. 1993;329:936-947

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

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