Babesia – Serology

NOTICE: Expected delay in Babesia Serology Turnaround Time (TAT)

Due to reagent supply issues at the National Reference Centre for Parasitology (NRCP), Babesia serology is currently delayed and is expected to resume to normal by the end of April 2024. The delayed turnaround time (TAT) is expected to be six to eight weeks past the stated TAT. For suspected Babesia cases, the preferred testing methodology remains microscopy and PCR as per this Public Health Ontario webpage: Babesia – Microscopy and PCR.

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

This page provides routine serology (antibody) testing information for babesiosis at Public Health Ontario (PHO). The causative agents of human babesiosis include Babesia microti (Northeastern and Midwestern US, East Asia, Europe, Australia), Babesia duncani (Western US), Babesia divergens (Europe), Babesia venatorum (Europe, China), and rarely other species. Currently, only serology for Babesia microti is available at PHO.

The test information described here is limited to serologic testing. For microscopic examination and PCR, please refer to the following link:

Effective July 1, 2023, babesiosis was added under the list of diseases of public health significance (DoPHS) in Ontario. Positive results are reported to the Medical Officer of Health as per Health Protection and Promotion Act. Additional testing and management recommendations are stated in the Infectious Disease Protocol Appendix 1 for Disease: Babesiosis.

Testing Indications

Microscopy and PCR are the gold standard diagnostic tests for babesiosis and should be requested whenever testing is indicated. Serologic testing is only an adjunct test to microscopy and PCR for individuals with clinical or epidemiologic risk factors for babesiosis.

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

5.0 ml blood

1.0 ml serum

Blood, clotted - vacutainer tubes (SST)

Submission and Collection Notes

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 or if asymptomatic
  4. Tick bite exposure, transfusion, transplantation, and/or perinatal history

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 rejection or testing delay.

Timing of Specimen Collection

An acute (collected early after the onset of symptoms) and a convalescent (collected 2-3 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 serum separator tube (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)

Babesia microti serology testing 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.

Serology testing for other Babesia species (e.g. B. duncani, B. divergens) is currently not available in Ontario.

Test Methods

Method: Babesia microti serology testing 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 severe immunosuppression, or in patients with asplenia. 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 be useful to distinguish acute from chronic/remote 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.1


If Babesia serology is requested without specifying the suspected species, or if Babesia microti serology is requested, samples will be forwarded to NRCP for Babesia microti testing and results will be returned to PHO’s laboratory to be reported to the physician.


Babesia microti IFA performed at the NRCP:

Babesia microti IFA titre


< 1/64


≥ 1/64



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.


  1. 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.
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Updated 2 Feb 2024