Babesia microti - Serology

Conformément au Règlement de l’Ontario 671/92 de la Loi sur les services en français, les renseignements d’analyses de laboratoire liés à la présente page ne sont offerts qu’en anglais parce qu’ils sont de nature scientifique ou technique et destinés uniquement à l’usage des fournisseurs de soins de santé qualifiés et non aux membres du public.

Babesia serology is not the recommended testing method for diagnosis of acute babesiosis. If babesiosis is suspected, submit EDTA blood and unstained slides for Babesia microscopy as per the following link: Babesia – Microscopy and PCR.

As a disease of public health significance (DoPHS) in Ontario, additional testing and management recommendations for babesiosis are stated in the Infectious Disease Protocol Appendix 1 for Disease: Babesiosis.

Effective May 31, 2024, Babesia microti serology is no longer routinely available through Public Health Ontario’s (PHO) laboratory and requires approval prior to submission.

Testing Indications

As per the most recent Infectious Diseases Society of America (IDSA) guidelines, Babesia microti serology should not be used for routine diagnosis of acute babesiosis.1 Its role is primarily limited to individuals linked to a case of transfusion-transmitted, transplant-associated, or congenital babesiosis with negative microscopy and PCR results.

Acceptance/Rejection Criteria

Serologic testing for Babesia is not performed routinely, and must be pre-approved by the PHO microbiologist before submission. Contact PHO’s Laboratory Customer Service at 416-235-6556 or 1-877-604-4567 for pre-approval.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit
Babesia or babesiosis or Babesia microti serology

Blood or serum

(must be pre-approved by PHO microbiologist prior to submission)

5.0 ml blood or 1.0 ml serum

Blood, clotted Serum separator tube (SST)

Submission and Collection Notes


Babesia serology is not performed routinely and must be pre-approved by a PHO microbiologist before submission. Contact PHO’s Laboratory Customer Service Centre at 416-235-6556 or 1-877-604-4567 for pre-approval. Failure to obtain pre-approval will result in test cancellation.


Complete all fields of the requisition form, including:

  1. Test(s) requests and indications for testing
  2. Patient setting/population
  3. Clinical information including symptom onset date
  4. Tick bite exposure, transfusion, transplantation, and/or perinatal history
  5. Recent Babesia microscopy and PCR test results

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in test cancellation or testing delay.

Timing of Specimen Collection

An acute (collected early after the onset of symptoms) and a convalescent (collected 2 to 4 weeks later) specimen may be required to complete laboratory investigations.


Grossly haemolysed, lipemic, contaminated specimens and specimens containing anti-coagulant are unsuitable for testing.

Storage and Transport

Centrifuge tube if using SST. Specimens should be stored at 2-8°C following collection and shipped on ice packs to PHO’s laboratory as soon as possible. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act .

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

If approved by PHO, Babesia microti serology is forwarded to the National Reference Centre for Parasitology (NRCP) in Montreal. Turnaround time is up to 30 days from receipt at PHO’s laboratory. Serologic testing for other Babesia species (e.g. B. duncani, B. divergens) is not available in Ontario.

Test Methods

Method: Babesia microti serology is performed by immunofluorescence assay (IFA).

Performance: The NRCP states a sensitivity of 100% and specificity of 99% in immunocompetent individuals. Other laboratories offering IFA have reported a sensitivity of 88 to 96% and specificity of 90 to 100%.1

Limitations: Serological antibody titres may be negative early in infection, in patients with impaired immunity, or in patients with impaired splenic function. False positive reactions may occur in patients with autoimmune disorders (e.g., rheumatoid arthritis). Antibody titres remain elevated for years following clearance of infection. Antibody titres ≥ 1:1024, or a four-fold increase in titres between acute and convalescent sera, may assist in distinguishing acute from chronic or past infection. Cross-reactivity may occur with Plasmodium spp. at lower antibody titre levels for IFA. Cross-reactivity is not usually reported between Babesia species-specific IFAs, therefore a negative Babesia microti IFA does not rule out infection with other Babesia species.2


Babesia microti IFA performed at the NRCP:

Babesia microti IgG IFA titre Result Interpretation
< 1/64 Negative No detectable level of IgG antibody against Babesia microti. This assay does not test for other Babesia species.
≥ 1/64 Positive Detectable level of IgG antibodies against Babesia microti. Cannot distinguish between acute and remote infection. Cross-reactivity may occur with Plasmodium spp.


Results are received back at PHO’s laboratory, and reports are forwarded to the ordering physician or authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Specimens that are positive for Babesia are to be reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.


  • Krause PJ, Auwaerter PG, Bannuru RR, Branda JA, Falck-Ytter YT, Lantos PM, Lavergne V, Meissner HC, Osani MC, Rips JG, Sood SK, Vannier E, Vaysbrot EE, Wormser GP. Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA): 2020 Guideline on Diagnosis and Management of Babesiosis. Clin Infect Dis. 2021 Jan 27;72(2):e49-e64. doi: 10.1093/cid/ciaa1216.
    Sanchez E, Vannier E, Wormser GP, Hu LT. Diagnosis, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis, and Babesiosis: A Review. JAMA. 2016 Apr 26;315(16):1767-77. doi: 10.1001/jama.2016.2884.
Mis à jour le 31 mai 2024