Babesia ImmunoBlot IgG (IGeneX)
The Babesia ImmunoBlot IgG test from IGeneX detects band-specific IgG antibodies against Babesia microti and Babesia duncani antigens in serum using an immunoblot format, providing expanded dual-species tick-borne haemoprotozoan serology beyond the coverage of standard CDC-referenced Babesia IFA testing.
2
Biomarkers
Blood (serum)
Sample
7–14 business days
Turnaround
No
Fasting
What is the Babesia IgG ImmunoBlot test?
The Babesia ImmunoBlot IgG test from IGeneX detects IgG antibodies against Babesia species antigens in serum using an immunoblot format — separating Babesia proteins by molecular weight on nitrocellulose membrane and reporting reactivity to individual antigenic bands. IGeneX is a specialty tick-borne disease reference laboratory known for its expanded species coverage and band-level reporting that exceeds the scope of standard CDC-referenced Babesia serology. The panel covers the two primary pathogenic Babesia species in North America — Babesia microti (northeastern and upper midwestern United States, Ixodes scapularis vector) and Babesia duncani (western United States, Ixodes pacificus vector) — within a single panel order, providing comprehensive species-level serological characterisation not available through standard reference laboratory Babesia testing. In mainstream infectious disease practice, Babesia diagnosis is established through direct detection methods — peripheral blood smear microscopy (ring forms and tetrads within erythrocytes), PCR amplification of Babesia DNA, and fluorescence in situ hybridisation (FISH) — with serology used as a confirmatory adjunct. The CDC-referenced standard serological method is indirect fluorescent antibody (IFA) testing, not immunoblot. IGeneX's immunoblot format, by contrast, provides band-specific serological data and is used primarily in the integrative and chronic tick-borne illness clinical context — particularly in patients presenting with complex multi-system symptoms in Lyme-endemic areas, in whom tick-borne co-infection evaluation requires expanded species coverage and serological sensitivity beyond standard two-tier testing. Practitioners should be aware that IGeneX's immunoblot positivity criteria and species coverage differ from CDC-referenced IFA standards, and that positive immunoblot results should be interpreted in concert with clinical presentation, haematological findings, and direct detection methods rather than used in isolation as diagnostic of active babesiosis. The IgG class specifically indicates an established immune response consistent with past exposure or ongoing infection — IgM testing is the complementary early-infection marker and should be ordered alongside IgG when acute babesiosis within the preceding 4–8 weeks is a clinical consideration.
What does the Babesia IgG ImmunoBlot test measure?
Babesia microti is an obligate intraerythrocytic apicomplexan parasite and the causative agent of the majority of human babesiosis cases in the northeastern and upper midwestern United States. It is transmitted by the bite of the black-legged tick Ixodes scapularis — the same vector responsible for Lyme disease (B. burgdorferi) and anaplasmosis (Anaplasma phagocytophilum) transmission — making co-infection a clinically important consideration in any Babesia-positive patient. IgG antibodies to B. microti antigens develop 2–4 weeks after infection, with IgM typically preceding IgG by 1–2 weeks. IgG can persist for years following both treated and untreated infection, limiting its utility as a sole indicator of active disease. The BMN (Babesia microti antigen) protein band is a species-specific antigen target in IGeneX's assay that provides serological discrimination from other Babesia species and cross-reactive organisms.
B. microti IgG ImmunoBlot seropositivity indicates prior or current immune exposure to B. microti and is a confirmatory marker in patients with a clinical presentation consistent with babesiosis — haemolytic anaemia, cyclical fevers, chills, night sweats, fatigue, and splenomegaly — following tick exposure in an endemic area. Because IgG persists long after infection, a positive result does not independently confirm active disease; correlation with clinical symptoms, full blood count (haemolytic pattern), peripheral blood smear, and B. microti PCR is required for establishing active infection. In patients with chronic multi-system tick-borne illness presentations, B. microti IgG ImmunoBlot provides serological evidence of prior Babesia exposure to complement the broader tick-borne co-infection workup.
Babesia duncani (previously designated WA1) is a piroplasm distinct from B. microti that causes human babesiosis primarily on the western coast of North America — California, Oregon, and Washington — transmitted by Ixodes pacificus, the western black-legged tick. B. duncani is antigenically distinct from B. microti, meaning standard B. microti IFA and immunoblot assays do not reliably detect B. duncani-specific antibodies, and separate species-specific antigen testing is required for detection. B. duncani has been associated with more severe and rapidly progressive babesiosis than B. microti, including fatality in immunocompetent individuals in published case series.
B. duncani IgG ImmunoBlot seropositivity is specifically relevant in patients with compatible clinical presentations who have tick exposure history in western North American endemic areas, or in patients from any region in whom B. microti testing is negative but clinical suspicion for tick-borne haemolytic illness remains. IGeneX's inclusion of B. duncani testing within the Babesia ImmunoBlot panel provides clinically meaningful geographic coverage that standard single-species Babesia serology — calibrated only for B. microti — would miss. Interpretation follows the same clinical correlation principles as B. microti IgG: positive serology requires correlation with active haematological findings, symptom history, and PCR before attributing active infection.
Why is the Babesia IgG ImmunoBlot test ordered?
- Suspected active babesiosis in Lyme-endemic areas — patients presenting with haemolytic anaemia, cyclical fevers, profuse night sweats, chills, fatigue, and splenomegaly following tick exposure or in a tick-endemic geographic area, where Babesia IgG ImmunoBlot is ordered alongside smear, PCR, and full blood count
- Tick-borne co-infection panel completion in patients with confirmed or suspected Lyme disease — given that Ixodes ticks co-transmit B. burgdorferi and B. microti, Babesia serology is a standard component of comprehensive tick-borne co-infection evaluation alongside Anaplasma, Ehrlichia, and Bartonella testing
- Chronic multi-system tick-borne illness workup — patients with persistent unexplained fatigue, haematological abnormalities, night sweats, air hunger, or cognitive symptoms in Lyme-endemic areas who have not responded to Lyme-directed antibiotic therapy and require expanded co-infection serological evaluation
- Western United States tick exposure — patients with tick exposure history in California, Oregon, or Washington where B. duncani (WA1) is the primary pathogenic species and is not detected by standard B. microti IFA testing, making IGeneX's dual-species immunoblot the appropriate diagnostic approach
- Immunocompromised patient assessment — asplenic, HIV-positive, organ transplant, or haematologically immunocompromised patients in tick-endemic areas where Babesia causes disproportionately severe and potentially fatal haemolytic illness, warranting expanded serological and direct detection screening even in the absence of acute febrile presentation
- Pre-blood or organ donation infectious disease screening in endemic regions — Babesia is transmissible via blood transfusion and has caused transfusion-transmitted babesiosis in regions where tick-borne Babesia is endemic, warranting donor screening in high-prevalence geographic areas # REVIEWER FLAG: Confirm appropriate clinical framing for donor screening context — transfusion-transmitted Babesia screening protocols are currently regulated and evolving.
- Post-treatment follow-up serology — confirming prior Babesia exposure in patients with resolved or treated babesiosis where documentation of serological status is required for clinical records, insurance, or occupational health purposes, with the understanding that IgG persists for years after resolution
- Integrative and functional medicine practitioners evaluating persistent symptoms in patients with known tick exposure history — comprehensive tick-borne co-infection panel including Babesia ImmunoBlot IgG/IgM, Lyme Western Blot, Anaplasma, Ehrlichia, and Bartonella serology
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
7–14 business days
Collection notes
Standard venipuncture into a serum separator tube (SST / gold top). No fasting or special preparation required. Practitioners must document on the IGeneX requisition form: (1) symptom onset date and duration; (2) tick exposure history — date, geographic location, and tick species if identified; (3) geographic residence and recent travel to Babesia-endemic areas (northeastern and upper midwestern USA for B. microti; western USA for B. duncani); (4) prior antibiotic treatment for tick-borne illness; (5) immunosuppressive medications or immunocompromising conditions; (6) blood transfusion history — relevant for transfusion-transmitted Babesia; (7) concurrent tick-borne co-infection testing being ordered. Specimen must be shipped to IGeneX per their cold-chain and specimen handling guidelines — confirm exact shipping requirements with IGeneX before first order. # REVIEWER FLAG: Confirm exact tube type, minimum serum volume, shipping temperature, and any special handling requirements with IGeneX specimen collection documentation before publication.
Specimen requirements
Minimum 1.0 mL serum. Centrifuge and separate serum from cells within 2 hours of collection. Stable at 2–8°C for up to 5 days; stable frozen at −20°C for extended storage. Ship per IGeneX cold-chain protocol. # REVIEWER FLAG: Confirm minimum volume and stability data with IGeneX assay documentation.
What can affect Babesia IgG ImmunoBlot results?
Antigenic cross-reactivity between Babesia species and other apicomplexan or haemoprotozoan organisms — including Plasmodium (malaria) and Theileria — may produce non-specific band reactivity on Babesia immunoblot, particularly at conserved protein positions such as heat shock proteins. Travel history to malaria-endemic regions should be documented; concurrent malaria testing should be considered when cross-reactivity is suspected.
Polyclonal B-cell activation and systemic immune stimulation during concurrent tick-borne co-infections — particularly B. burgdorferi — may generate non-specific antibody reactivity that could produce low-level band reactivity on Babesia immunoblot not attributable to true Babesia-specific antibody. Results must always be interpreted in the context of the full co-infection panel and the clinical presentation, not as isolated serological findings.
IgG class switching and seroconversion following B. microti or B. duncani infection requires 2–4 weeks, with IgM typically detectable 1–2 weeks earlier. Specimens collected within the first 2–4 weeks of symptom onset may return seronegative or indeterminate IgG results despite active infection. When acute babesiosis is suspected within this window, direct detection methods — peripheral blood smear and PCR — take diagnostic precedence over serology. Paired acute and convalescent serology 2–4 weeks apart is the appropriate serological approach in early presentations.
Pharmacological immunosuppression, haematological malignancy, HIV, or primary antibody deficiency can impair B cell-mediated antibody production, producing seronegative or weak-positive immunoblot results despite active or prior Babesia infection. In immunocompromised patients, direct detection by PCR and blood smear is more reliable than serology, and seronegative results should not exclude Babesia from the differential in a symptomatic immunocompromised patient with tick exposure.
IgG antibodies to Babesia antigens can persist for years to decades following both treated and spontaneously resolved infection. A positive IgG ImmunoBlot result does not independently confirm currently active infection and may reflect remote prior exposure. Active babesiosis requires positive direct detection (smear, PCR) or a compatible acute haematological presentation in addition to seropositivity. Treatment decisions should not be based on serology alone in the absence of direct evidence of active infection or a compatible acute clinical syndrome.
Significant in vitro haemolysis releases erythrocyte contents — including haemoglobin and its breakdown products — which may interfere with immunoblot membrane binding and band intensity reading. Haemolysed specimens should be rejected and recollected per IGeneX specimen handling guidelines. Note that in vivo haemolysis from active babesiosis does not cause false positivity — haemolysis within the patient from Babesia-mediated erythrocyte destruction does not affect in vitro assay integrity when specimen collection is performed appropriately. # REVIEWER FLAG: Confirm IGeneX specimen rejection criteria for haemolysis.
What do Babesia IgG ImmunoBlot results mean?
Elevated
A positive Babesia ImmunoBlot IgG result indicates serological evidence of prior immune exposure to the respective Babesia species. In a patient presenting with compatible clinical features — haemolytic anaemia, cyclical fevers, night sweats, fatigue, splenomegaly — and tick exposure history in an endemic area, a positive IgG ImmunoBlot provides supportive serological evidence of babesiosis. However, IgG positivity alone does not confirm active infection — direct detection by peripheral blood smear and PCR is required for active disease confirmation. In asymptomatic patients or those with remote tick exposure, IgG positivity most likely reflects prior resolved or treated infection rather than active disease requiring treatment. Positive B. duncani IgG in a patient from a non-western geographic area should prompt careful exposure history review — travel to the western USA, blood transfusion history, or unusual tick exposure may explain the finding.
Normal
A fully negative Babesia IgG ImmunoBlot in an immunocompetent patient with symptoms beyond 4–6 weeks in duration and no other haematological evidence of active haemolysis substantially reduces the probability of significant Babesia co-infection. Alternative diagnoses — including other tick-borne pathogens, viral illness, or non-infectious haematological conditions — should be evaluated when Babesia serology is negative and symptoms persist. Babesia IgM should be added to the workup when early acute babesiosis within the preceding 4–8 weeks cannot be excluded.
Reduced
A negative Babesia IgG ImmunoBlot result indicates no detectable IgG antibodies to the tested Babesia species antigens at the time of collection. In a patient with acute presentation within the first 2–4 weeks of tick exposure, IgG seronegative status does not exclude early babesiosis — peripheral blood smear and PCR are the appropriate diagnostic tests in this window, as IgG seroconversion has not yet occurred. In patients with longer-duration symptoms and negative serology, babesiosis is less likely but not fully excluded in strongly endemic areas with high clinical suspicion; repeat convalescent serology and PCR should be considered. Immunocompromised patients may remain seronegative despite active infection due to impaired antibody production.
Note: The most important interpretive caveat is that IgG ImmunoBlot seropositivity confirms prior immune exposure to Babesia but cannot establish that active Babesia infection is the current cause of the patient's symptoms — IgG can persist for years after resolved infection. Active babesiosis requires direct microbiological evidence (positive smear, PCR, or FISH) or a compatible acute haematological presentation in a patient with plausible tick exposure history and haematological findings consistent with haemolytic anaemia. Additionally, IGeneX's immunoblot methodology and positivity criteria differ from CDC-referenced IFA standards and have not undergone the same level of independent prospective clinical validation — practitioners should be aware of this when applying IGeneX results to clinical decision-making, and positive results should be contextualised alongside the full clinical picture rather than treated as definitive confirmation of active disease. The expanded band-level reporting from IGeneX may identify low-level reactive patterns not meeting CDC IFA positivity thresholds — the clinical significance of such patterns in asymptomatic or minimally symptomatic patients requires careful clinical judgement.
Frequently asked questions
The Babesia IgG ImmunoBlot from IGeneX detects band-specific IgG antibodies against Babesia microti and Babesia duncani antigens in serum. The immunoblot format separates Babesia proteins by molecular weight, identifying which specific antigenic bands elicit an immune response. This provides species-level discrimination and dual-species coverage — B. microti (northeastern and upper midwestern USA) and B. duncani (western USA) — that is not available through standard single-species Babesia IFA testing.
How to access the Babesia IgG ImmunoBlot test
The Babesia IgG ImmunoBlot 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.
Create Free AccountAbout this page
Published: May 23, 2026
Last reviewed: May 23, 2026
- Vannier EG, et al. Babesiosis. Infect Dis Clin North Am. (2015)
- Krause PJ, et al. Persistent and relapsing babesiosis in immunocompromised patients. Clin Infect Dis. (1998)
- Herwaldt BL, et al. Transmission of Babesia microti in the United States. Emerg Infect Dis. (2012)
- Lantos PM, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America: 2020 Guidelines for the Prevention, Diagnosis and Treatment of Lyme Disease. Clin Infect Dis. (2021)
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.
Related tests
lyme tick borne
Babesia IgM
The Babesia ImmunoBlot IgM detects acute-phase antibodies to Babesia species using species-specific antigen bands, aiding diagnosis of tick-borne babesiosis and co-infection with Lyme disease. Positive results support recent or active infection when correlated with clinical presentation, haemolytic anaemia, and parasitology or PCR confirmation.
infectious disease
Lyme Western Blot (IgG/IgM)
The B. burgdorferi IgG and IgM Western Blot detects band-specific serum antibodies to Borrelia burgdorferi antigens by molecular weight, serving as the confirmatory tier-two assay in the two-tier Lyme disease testing algorithm following a positive or equivocal ELISA screen. IgM Western Blot is the appropriate early marker within the first four weeks of symptom onset;