HIV – Diagnostic Serology

Testing Indications

If ordering as part of a Prenatal Serology work-up, see Prenatal – Serology.

Limitations

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

Storage and Transport

Label the specimen container with the patient’s full 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.

Special Instructions

Centrifuge if using SST. Place specimen in biohazard bag and seal. Specimens should be stored at 2-8°C following collection and shipped to PHO Laboratory on ice packs.

Specimens may be stored on or off the clot or red blood cells for up to 7 days at 2-8°C. If testing will be delayed more than 7 days, remove serum or plasma from the clot and store frozen at -20°C or colder.

Test Frequency and Turnaround Time (TAT)

HIV diagnostic serology testing is performed daily Monday to Friday.

Turnaround time is up to 3 days for non-reactive samples and up to 6 days for reactive samples from receipt by PHO laboratory.

Stat and Critical Samples Testing

Testing of ‘source patient’ for needlestick/occupational exposure if warranted.
Testing of pregnant women in labour with no prenatal work up and a high risk for HIV.

STAT testing should only be requested when it directly affects patient care in an emergency medical circumstance. STAT samples must be shipped separately from routine specimens in a clearly marked package indicating ‘STAT’ and 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.

Notify PHO immediately when a STAT sample is sent by contacting our Customer Service Centre at 416-235-6556 / 1-877-604-4567. After-hours STAT testing requires approval by a PHO Microbiologist who can be contacted through the Customer Service Centre.

Specimens are screened for Human Immunodeficiency Virus (HIV) using a chemiluminescent micro-particle immunoassay (CMIA) for the simultaneous qualitative detection of HIV p24 antigen (Ag) and antibodies to HIV-1 and/or HIV-2, but does not differentiate between the two.

If the CMIA test is reactive or indeterminate, the specimen is tested using the Geenius^TM HIV1/2 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^TM HIV1/2 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.

Algorithm

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.

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition.

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

References

LAB-SD-008, Blood Collection Using Serum Separator Tubes