Why does this panel test for two Babesia species?

B. microti is endemic to the Northeast and Upper Midwest, while B. duncani predominates in the Pacific Northwest. Testing for both species increases diagnostic sensitivity and helps identify the geographic source of infection, which is useful when travel history is complex or when regional co-infection patterns differ.

Can serology detect babesiosis in the first week of illness?

No. Antibodies to Babesia typically do not appear until two to four weeks after infection, so early serology is often falsely negative. Paired acute and convalescent specimens or direct methods (thin-film microscopy, PCR) are recommended when early infection is suspected.

Does a positive Babesia result mean the infection is currently active?

Not necessarily. IgG can persist for years after successful treatment, so positive serology indicates current or past infection. Active infection is supported by positive IgM, rising titres in paired sera, compatible clinical features, and, ideally, molecular or microscopic confirmation of parasites.

Is fasting required for the Babesia Panel 2B?

No. This serology does not require fasting, though practitioners may order it alongside tests that do.

Why is this test performed by a specialty laboratory?

IgeneX specialises in tick-borne disease diagnostics and uses proprietary antigens and thresholds that are validated specifically for Babesia serology. Results are not directly comparable to other platforms, and interpretation should reference IgeneX's cutoffs and clinical validation data.

Can Babesia serology cross-react with malaria?

Yes. Shared epitopes between Babesia and Plasmodium species can produce low-level cross-reactivity, particularly in individuals with past malaria exposure. Clinical and travel history are essential to interpretation.

What should be done if serology is negative but clinical suspicion remains high?

Repeat serology in two to four weeks to allow for seroconversion, and consider direct detection methods such as thin-film microscopy or Babesia PCR. In immunocompromised or asplenic patients, negative serology does not exclude babesiosis.

How long do results take?

Results are typically available within 7–10 business days from specimen receipt at IgeneX, though turnaround may be longer during peak tick season.

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Babesia Panel 2B (BAB2B)

The Babesia Panel 2B detects IgG and IgM antibodies to B. microti and B. duncani, the two most clinically significant Babesia species in North America. It supports the diagnosis of babesiosis in patients with fever, haemolytic anaemia, and tick exposure, and is central to evaluating co-infection with Lyme disease, though serology is method-dependent and must be interpreted with clinical context…

Biomarkers

Blood (serum)

Sample

7–10 business days

Turnaround

Fasting

What is the BAB2B test?

The Babesia Panel 2B is a serological assay that detects IgG and IgM antibodies to the two most clinically significant Babesia species in North America: B. microti (prevalent in the Northeast and Upper Midwest) and B. duncani (endemic to the Pacific Northwest). Babesiosis is an emerging tick-borne infection that causes fever, haemolytic anaemia, and constitutional symptoms and can be severe or fatal in asplenic, elderly, or immunocompromised individuals. Because parasitaemia is often low and intermittent, serology is a central diagnostic tool when direct methods are negative or impractical. Practitioners order this panel when clinical, epidemiological, and laboratory features suggest babesiosis — fever, sweats, haemolytic anaemia, thrombocytopenia, and a history of tick exposure or residence in an endemic area — and when Babesia co-infection is suspected in patients with confirmed or probable Lyme disease, given the shared Ixodes vector. The panel's inclusion of both species and both immunoglobulin classes increases diagnostic yield and helps localise the likely species exposure, though cross-reactivity and the lag between infection and seroconversion mean that serology complements rather than replaces parasitological and molecular methods.

What does the BAB2B test measure?

B. microti IgG(Babesia microti IgG Antibody)

Range: Negative <1.0; Equivocal 1.0–1.2; Positive >1.2 (IgeneX method-specific).Optimal: Negative in individuals without exposure. Seropositivity is consistent with past or current infection; rising titres in paired sera suggest recent infection.Index / Titre

IgG antibodies to Babesia microti appear several weeks after infection with this intraerythrocytic apicomplexan parasite, which is transmitted by Ixodes ticks and causes fever, haemolytic anaemia, and constitutional symptoms. IgG persists for months to years after acute infection and is the mainstay of serological diagnosis, though cross-reactivity with other Babesia species and Plasmodium can occur.

IgG serology supports the diagnosis of current or past B. microti infection in patients with compatible clinical and epidemiological features. It is particularly useful when direct parasitological methods (thin-film microscopy, PCR) are negative or unavailable. Persistent IgG does not distinguish active from resolved infection, so serology is interpreted alongside clinical course and, where possible, molecular or microscopic confirmation.

B. duncani IgG(Babesia duncani IgG Antibody)

Range: Negative <1.0; Equivocal 1.0–1.2; Positive >1.2 (IgeneX method-specific).Optimal: Negative in individuals without exposure. Positive results support clinical babesiosis in the appropriate epidemiological context.Index / Titre

Babesia duncani (formerly WA1) is a distinct Babesia species endemic to the western United States. Like B. microti, it is an intraerythrocytic parasite that elicits IgG responses detectable weeks after infection. The humoral response to B. duncani shows partial cross-reactivity with B. microti but can be distinguished by species-specific antigens.

B. duncani serology is essential in regions where this species predominates, particularly the Pacific Northwest. It complements B. microti testing in a comprehensive tick-borne panel and is critical when clinical babesiosis is suspected in a patient with travel or residence in western endemic areas.

B. microti IgM(Babesia microti IgM Antibody)

Range: Negative <1.0; Equivocal 1.0–1.2; Positive >1.2 (IgeneX method-specific).Optimal: Negative in unexposed or recovered individuals. Positive IgM with positive IgG supports acute or recent infection.Index / Titre

IgM antibodies to B. microti appear early in the course of infection, typically within the first weeks, and decline over months. IgM is less sensitive than IgG for chronic or low-level infection and can be absent in immunocompromised patients or reactivated disease.

IgM is a marker of acute or recent infection. Its presence alongside IgG increases the specificity of serological diagnosis in the acute phase, though false-negative IgM is common once the infection becomes subacute or chronic. IgM must be interpreted cautiously because cross-reactivity and prolonged low-level positivity can occur.

B. duncani IgM(Babesia duncani IgM Antibody)

Range: Negative <1.0; Equivocal 1.0–1.2; Positive >1.2 (IgeneX method-specific).Optimal: Negative in unexposed or recovered individuals. Positive IgM with positive IgG is consistent with acute B. duncani infection.Index / Titre

IgM to B. duncani, like IgM to B. microti, is a marker of early immune response. Its kinetics parallel those of B. microti IgM, though data on persistence and false-negative rates are sparser given the lower incidence of B. duncani infection.

Detection of B. duncani IgM supports acute infection with this species. It is most useful in the first weeks of illness and in conjunction with IgG serology and clinical context. As with all IgM assays, sensitivity is lower than that of IgG, and negative IgM does not exclude infection.

Why is the BAB2B test ordered?

Febrile illness with haemolytic anaemia, thrombocytopenia, or elevated indirect bilirubin in a patient with tick exposure or residence in an endemic region
Suspected co-infection with Lyme disease, particularly when constitutional symptoms are disproportionate to erythema migrans or when treatment response is incomplete
Work-up of unexplained fever in asplenic, elderly, or immunocompromised patients with possible tick exposure, given the risk of severe babesiosis in these groups
Differential diagnosis of malaria in a returned traveller when thin-film microscopy suggests intraerythrocytic parasites but travel history does not fit Plasmodium endemicity
Screening of blood donors in endemic areas, where serological and molecular testing are used to reduce transfusion-transmitted babesiosis
Chronic fatigue, arthralgias, or other non-specific symptoms in a patient with documented tick exposure when a comprehensive tick-borne panel is warranted
Regional tailoring of babesiosis testing — this panel is indicated when B. duncani exposure (western United States) is possible alongside or instead of B. microti
Follow-up serology in patients with initial negative results when clinical suspicion remains high, because seroconversion may be delayed by weeks

Sample collection and turnaround

Sample type

Blood (serum)

Fasting required

Collection method

Venipuncture at patient service centre

Turnaround

7–10 business days

Collection notes

Phlebotomy required; serum is separated and shipped to IgeneX. Practitioners should ensure that the patient has not been on antimicrobial therapy long enough to suppress antibody production if early infection is suspected, and consider paired acute and convalescent specimens (two to four weeks apart) when initial serology is negative but clinical suspicion persists.

Specimen requirements

Minimum 1 mL serum, separated and refrigerated. IgeneX provides specimen collection and shipping instructions; follow the laboratory's protocol for tube type and transport temperature.

What can affect BAB2B results?

variableTiming relative to symptom onset

Antibodies to Babesia may not appear until two to four weeks after infection, so early serology can be falsely negative; paired acute and convalescent specimens are recommended when initial results are negative.

reducesImmunosuppression and asplenia

Profoundly immunocompromised or asplenic patients may mount weak or absent antibody responses despite high parasitaemia, so negative serology does not exclude babesiosis in these populations.

elevatesCross-reactivity with other Babesia species and Plasmodium

Shared epitopes among Babesia species and between Babesia and malaria parasites can produce low-level cross-reactive positivity, particularly in individuals with past Plasmodium exposure.

elevatesPersistent seropositivity after treated infection

IgG can remain detectable for years after successful treatment, so a positive IgG does not confirm active infection; clinical correlation and, where needed, molecular or microscopic confirmation are essential.

variableAssay variability and lack of standardisation

Babesia serology is not standardised across laboratories, and IgeneX uses proprietary antigens and cutoffs that are not directly comparable to other platforms; results should be interpreted in the context of the performing laboratory's validation.

variableCo-infection with Borrelia or Anaplasma

Co-infection can modulate immune responses and complicate the clinical picture, so a comprehensive tick-borne panel is often more informative than Babesia serology alone.

What do BAB2B results mean?

Elevated

Positive IgG or IgM to B. microti or B. duncani is consistent with current or past infection. IgM positivity, particularly when accompanied by IgG, supports acute or recent infection, while isolated IgG suggests past exposure or chronic low-grade infection. Rising titres in paired sera strengthen the diagnosis. Positive serology in the appropriate clinical and epidemiological context (fever, haemolytic anaemia, tick exposure, endemic residence) warrants treatment, though molecular or microscopic confirmation is preferred when available. The species (microti vs duncani) that is seropositive can suggest the geographic source of infection.

Normal

Negative IgG and IgM to both B. microti and B. duncani make babesiosis less likely in an immunocompetent patient beyond the window of seroconversion, but do not exclude it definitively. Interpret alongside clinical features, complete blood count (anaemia, thrombocytopenia), and, when indicated, parasitological studies.

Reduced

Negative serology does not exclude babesiosis, particularly in early infection (before seroconversion), in immunocompromised or asplenic patients with impaired antibody responses, or when parasitaemia is low. If clinical suspicion is high, repeat serology in two to four weeks and consider direct methods (thin-film microscopy, PCR) to detect parasites.

Note: Serology is method- and laboratory-dependent; IgeneX thresholds and reference ranges are proprietary and not interchangeable with other platforms. Cross-reactivity with other Babesia species and Plasmodium can occur. Persistent IgG seropositivity is common after treated infection, so positive serology alone does not confirm active disease — correlation with clinical course, PCR, or blood-film examination is essential. Co-infection with Borrelia burgdorferi or Anaplasma phagocytophilum is frequent and should be considered in the diagnostic work-up.

Frequently asked questions

Babesiosis is a tick-borne infection caused by intraerythrocytic parasites, primarily B. microti and B. duncani in North America. It causes fever, haemolytic anaemia, and constitutional symptoms and can be severe or fatal in asplenic, elderly, or immunocompromised patients. Testing is important because clinical features overlap with other tick-borne diseases and direct parasitological methods can miss low-level infections.

How to access the BAB2B test

The BAB2B reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.

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About this page

Published: October 7, 2026

Last reviewed: October 7, 2026

References:

Krause PJ, et al. Clinical practice guidelines by the Infectious Diseases Society of America (IDSA): 2020 guideline on diagnosis and management of babesiosis. Clin Infect Dis. (2021)
Vannier EG, Krause PJ. Human babesiosis. N Engl J Med. (2012)
Wormser GP, et al. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. (2006)
Leiby DA. Transfusion-transmitted Babesia spp.: bull's-eye on Babesia microti. Clin Microbiol Rev. (2011)
Telford SR III, et al. Perpetuation of the agent of human granulocytic ehrlichiosis in a deer tick-rodent cycle. Proc Natl Acad Sci USA. (1996)

This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.