When to test after a possible exposure to HIV14
It is important to understand HIV testing window periods when considering an HIV test after a possible exposure. Traditionally, waiting 3 months after exposure was recommended; however, newer 4th generation HIV tests have shortened the window period. The average window period for 4th generation enzyme immunoassays (EIA) tests (which detect p24 antigen and HIV antibodies) is 16-18 days.
Diagnostic methods and technologies continue to evolve and the window period may be shortened in the future.
Most patients can be tested at 4 weeks following exposure (>95% of infected individuals will have detectable antibodies at this time). If negative, repeat testing at 3 months is recommended (>99% of infected individuals will have a positive EIA at this time).
If a recent high-risk exposure has occurred, or acute HIV infection (seroconversion) is suspected, test now. Please indicate “query acute HIV” on the laboratory requisition. Molecular detection methods can be added to standard serology.
Results of these tests require interpretation within the clinical and epidemiological context of the patient. A negative result in an individual with a high likelihood of being HIV positive can be reviewed with the medical microbiologist responsible for the testing laboratory.
Non-nominal reporting is available in British Columbia, meaning that the full name of the individual is not reported to public health. The first name, initials, and date of birth are reported to the Medical Health Officer for surveillance purposes. The full name of the individual is still on the specimen sent to the laboratory.
Other Testing Options
Occasionally, providers may encounter a patient who has concerns about confidentiality in HIV testing.
Testing using an alias or initials only is available at certain sites in British Columbia. See: http://smartsexresource.com/get-tested/hiv-testing
A pilot of anonymous testing is underway in British Columbia. With an anonymous HIV test, the test is identified by a code known only to the patient. No identifiable or contact information is collected and the person being tested must provide his or her anonymous testing code in order to receive the result.
Patients seeking an anonymous HIV test can access this test by: http://smartsexresource.com/topics/hiv-anonymous-testing
These forms of testing are not ideal from a public health perspective. However, if confidentiality is a barrier to testing, these options are available.
Point of Care Testing
In British Columbia, point of care testing is used in outreach setting. It has a similar sensitivity to traditional 3rd generation HIV testing. Confirmatory testing is required for indeterminate, invalid, and preliminary positive results. Point of care testing is insufficient to rule out acute HIV infection and is not recommended for those with a recent exposure.
For more information on POC testing, please see: