HIV – Diagnostic Serology

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 diagnostic serology testing information for HIV at Public Health Ontario (PHO). For information regarding other testing options, refer to the following PHO webpages:

Testing Indications

HIV testing should be considered in individuals:

  • with symptoms of acute HIV infection
  • with symptoms associated with chronic HIV infection
  • who have had a high-risk exposure
  • who belong to a population with higher rates of HIV
  • who are initiating immune suppressing therapy
  • who are pregnant; if ordering as part of a prenatal screening, see Prenatal – Serology

For more information on HIV testing recommendations, refer to the Ontario Guidelines for Providers Offering HIV Testing.

Acceptance/Rejection Criteria

  • Donor testing is not available through PHO’s laboratory. Specimens from patients being screened as potential donors (e.g. organ, tissue, cells, fertility, etc.) should be referred to a laboratory that performs donor screening assays. Specimens received for donor screening at PHO’s laboratory will be rejected.
  • Specimens received more than 7 days post collection will not be tested.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit



1.5 ml

Serum Separator Tube (SST)

Submission and Collection Notes


Complete all fields of the requisition form, including:

  1. Test(s) requests and reason for testing
  2. Patient setting, specimen type and site
  3. Relevant clinical information

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. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.


Submit centrifuged serum separator tubes (SST) for serological assays.


One FULL 5 mL SST is required for testing a combination of HIV, hepatitis virus, HTLV, syphilis and rubella.


Do not submit glass tubes.


Haemolysed, icteric, lipemic or microbially contaminated sera or plasma are not recommended for testing.

Storage and Transport

Place specimen tube in biohazard bag and seal. Place completed General Test Requisition in the pouch at the front of the biohazard bag.

Specimen tubes should be stored at 2-8°C following collection and centrifugation, and should be shipped to PHO’s laboratory on ice packs within 3 days of collection. If delayed shipping is anticipated, remove serum from clot and store frozen at -20°C or colder, and ship on dry ice.

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)

HIV diagnostic serology testing is performed daily Monday to Friday.

Turnaround time is up to 3 business days for non-reactive specimens and up to 6 business days for reactive specimens from receipt by PHO’s laboratory.

Stat and Critical Samples Testing

STAT testing should only be requested when it directly affects patient care in an emergency medical circumstance. If warranted, the following HIV testing is expedited:

  • Testing of the ‘source patient’ for needlestick/occupational exposure
  • Pregnant women presenting in labour who have not received prenatal care or for whom results of previous testing are not readily available and are a high risk for HIV

STAT samples must be shipped separately from routine specimens and delivered to PHO’s laboratory in a timely manner. The outer package must be clearly marked indicating ‘STAT’. It must be handled in accordance with the Canadian Biosafety Standards and shipped in accordance with the Transportation of Dangerous Goods Regulations. Failure to ship separately will delay testing.

Prior to sending, notify PHO’s laboratory Customer Service Centre at 416-235-6556 / 1-877-604-4567. After-hours STAT testing requires approval by a PHO Microbiologist. Contact the After-Hours Emergency Duty Officer at 416-605-3113 if outside of PHO’s laboratory operating hours.

Test Methods

Specimens are screened for human immunodeficiency virus (HIV) using a chemiluminescent microparticle immunoassay (CMIA) for the simultaneous qualitative detection of HIV-1 p24 antigen (Ag) and antibodies to HIV-1 and HIV-2, but does not differentiate between the two.

If the CMIA test is reactive or indeterminate, the specimen is tested using the Geenius™ HIV-1/-2 Differential assay, which is an immunochromatographic test for the confirmation and differentiation of antibodies to HIV-1 (Group M and O) and HIV-2.

CMIA-positive samples that are negative or indeterminate by the Geenius™ HIV-1/-2 Differential assay are screened for p24 Ag using an Enzyme Linked Fluorescent Assay (ELFA) for the detection of HIV-1 p24 Ag. Samples that are positive for p24 Ag are confirmed using a p24 Ag neutralization assay.


Results should be interpreted in the context of the patient’s clinical presentation, risk factors, and exposure history. The table below provides a general overview of the algorithm and most common interpretations for HIV screening and confirmatory testing. It does not include all possible result scenarios. A PHO Microbiologist is available for questions about HIV serology results and interpretations.

HIV Ab/Ag CMIA Screen

GeeniusTM Confirmatory Assay

p24 Ag ELFA



Not Tested

Not Tested

No HIV p24 antigen and no HIV-1/HIV-2 antibodies detected.




Not Tested

HIV-1 antibodies detected OR HIV-2 antibodies detected






Evidence of HIV-1 infection prior to seroconversion.







Inconclusive HIV p24 antigen and inconclusive HIV-1/HIV-2 antibodies.

Submit a follow-up specimen for repeat testing at least 4 weeks after collection of the first specimen.


Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

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

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Updated 5 May 2023