HIV – Diagnostic Serology

Testing Indications

HIV testing should be considered as part of routine care. Specifically, testing is recommended for 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.

Limitations

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

Storage and Transport

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

Store specimen tubes at 2-8°C following collection and centrifugation, and ship to PHO’s laboratory on ice packs within 3 days of collection. Ideally, centrifuge specimens within 24 hours 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 with the Transportation of Dangerous Good Act.

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.
• A pregnant individual presenting in labour who has not received prenatal care or for whom results of previous testing are not readily available and are at high risk for HIV.

Prior to sending, PHO’s laboratory Customer Service Centre must be notified at 416-235-6556 / 1-877-604-4567. 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.

After-hours STAT testing requires approval by a PHO Microbiologist. Contact the after-hours Duty Officer at 416-605-3113 if outside of PHO’s laboratory operating hours.

The following assays may be used for HIV diagnostic testing:

1. HIV-1/-2 antigen (Ag)/antibody (Ab) combination screen: Chemiluminescent microparticle immunoassay (CMIA) that simultaneously detects HIV-1 p24 Ag and HIV-1 and HIV-2 Ab. This assay does not differentiate between p24 and HIV-1/-2 Ab.
2. HIV-1/-2 antibody confirmatory test: Geenius™ immunochromatographic test for confirmation and differentiation of antibodies to HIV-1 and HIV-2.
3. HIV-1/-2 PCR: Qualitative nucleic acid test (NAT) for the qualitative detection and differentiation of HIV-1 and HIV-2 RNA.

Algorithm

Serum specimens submitted for HIV serology are tested following the algorithm below:

Interpretation

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 the most common interpretations for HIV diagnostic testing for adults. It does not include all possible result scenarios. These interpretations may not apply to infants as maternal antibodies can circulate for 18-24 months after birth. Consider referral to a paediatric HIV specialist for management of infants suspected of HIV infection.

HIV-1/HIV-2 Ag/Ab Combo Screen	HIV-1/HIV-2 Ab Confirmatory	HIV-1/HIV-2 PCR	Interpretation
Non-reactive	Not Tested	Not Tested*	No evidence of HIV infection. For high-risk exposures, repeat HIV testing at 3 weeks and, if negative, at 6 weeks after possible exposure or on presentation of symptoms compatible with acute HIV infection.   *HIV PCR is tested if “Symptoms - acute infection) (e.g. flu-like illness, fever, rash)” is selected or “window period” is indicated on the requisition.
Reactive/ Indeterminate	Negative/ Indeterminate	HIV-1 and HIV-2 RNA not detected	Inconclusive for HIV infection.   Repeat testing in at least 4 weeks from date of collection. If two or more inconclusive results have been obtained on separate specimens, no further testing for HIV is recommended unless clinically warranted.
Reactive/ Indeterminate	HIV-1 positive	Not Tested	Evidence of HIV-1 infection.
Reactive/ Indeterminate	HIV-2 positive	Not Tested	Evidence of HIV-2 infection.
Reactive/ Indeterminate	HIV-1 and HIV-2 positive	Not Tested	Evidence of HIV-1 and HIV-2 co-infection.
Reactive/ Indeterminate	Negative/ Indeterminate	HIV-1 RNA detected	Evidence of acute HIV-1 infection.
Reactive/ Indeterminate	Negative/ Indeterminate	HIV-2 RNA detected	Evidence of acute HIV-2 infection.
Reactive/ Indeterminate	Negative/ Indeterminate	HIV-1 and HIV-2 RNA detected	Evidence of acute HIV-1 and HIV-2 co-infection.

A PHO Microbiologist is available for questions about HIV serology results and interpretations by calling 416-235-6556 / 1-877-604-4567 or by email at CustomerServiceCentre@oahpp.ca.

For individuals who test positive for HIV, consider submitting a follow-up EDTA whole blood or plasma specimen for HIV-1 viral load testing. Refer to the HIV-1 Viral Load Test Information Sheet for detailed information.

Reporting

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.