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Materials in this module will help you: 

  • Know the difference between the rapid HIV test that screens for HIV and the standard laboratory testing that can confirm a diagnosis
  • Be able to explain the process of HIV infection and how it impacts the ability of tests to detect infection
  • Be able to recommend an appropriate strategy for testing to individuals in the window period
  • Understand the results of HIV testing

Rapid versus Standard Laboratory Testing in Ontario

 Rapid HIV TestingStandard Laboratory HIV Testing
How Ontario uses the TestAs a screening test to rapidly assess people for HIV; reactive results must be confirmed by laboratory testingMore than one test on any reactive result is done to diagnose infection; someone diagnosed with this test should begin treatment as soon as possible
What the test involvesCollection of a small amount of blood through a finger prickCollection of a tube of blood sent to the provincial laboratory
Delivers immediate negative results at the testing appointment; reactive results must be confirmedProvincial lab results usually return within one week. Client must follow-up for results (see your site’s policies for details)
A single test done in a few minutesMore than one test done on reactive results, to confirm a positive diagnosis
What is required for the testWhole bloodSerum
An approved POC testing facility, does not require a medical environmentAn accredited testing laboratory with complex equipment and maintenance
A trained POC testing counsellor (like you will be), acting under a medical directive from a regulated medical professionalAn accredited medical laboratory technologist
Careful quality control practicesCareful quality control practices
What the test measuresHIV antibodies (IgG and IgM)HIV antibodies (IgG and IgM) and p24 Ag (a component of the virus)
The accuracy of the tests (after the window period)Both the rapid and standard testing used in Ontario are highly accurate. Typically, there are two measures of a test’s accuracy – sensitivity and specificity.
99.6% sensitivity (% of HIV infections detected)100% sensitivity (% of HIV infections detected)
99.3% specificity (only HIV is detected)99.77% specificity (only HIV is detected)*

*This is the specificity for the first test used by the Public Health Labs of Ontario; positive results are confirmed with additional tests decreasing the possibility of a false positive.

The Timeline of HIV Infection

Derived from an image in Taylor D, Durigon M et al. Probability of a false-negative HIV antibody test result during the window period: a tool for pre- and post-test counselling. Inter J of STD & AIDS 2015;26(4):215-224. Available at https://bit.ly/2BnpiSG [downloaded November 19, 2018]   

The Symptoms of Acute HIV Infection

Some of these symptoms are experienced by 50-90% of people newly infected with HIV usually 2-4 weeks after exposure:

  • Fever is the most common symptom, above 38°C, but usually mild. Lasts about 1-2 weeks.
  • Other common “flu” symptoms happen with the fever: sore throat, headache, muscle and joint pain
  • Two-three days after the fever starts, a rash may develop. It usually affects the face, neck, and upper chest, but may be more widespread. It usually lasts 5-8 days and may or may not be itchy. It is most typically a flat red area covered with small bumps.
  • In the second week of fever, many people experience swollen lymph nodes. The swelling is usually painless and may linger.
  • About half of people who have symptoms may experience GI upset (nausea, vomiting, diarrhea)
From: Sax PE. Patient education: Symptoms of HIV infection (Beyond the Basics). UpToDate. Available at https://bit.ly/2DlmPJN [download November 13, 2018].   

A small proportion of people with signs of acute infection develop small open sores in/on the mouth, esophagus, genitals or anus. These are often painful.

The Window Period

Point of care testing focuses on working with clients from populations with increased risk of acquiring HIV to identify new infections as soon as possible, and to encourage people with negative tests to engage in prevention practices.

Key Messages for clients:

  1. Not everyone acquires HIV through a high-risk exposure. However, if infection occurs, the levels of virus rise quickly in the early stages. Advise abstinence, condoms and harm reduction to protect others while in the window period.
  2. Point-of-care testing can identify some new infections as early as three weeks after exposure, and will identify most new infections earlier than three months, however standard laboratory testing can measure antibodies and p24 antigen, and will identify 99% of new infections by 6 weeks.
  3. At three weeks (or any time while the client still has seroconversion symptoms), perform a rapid test if requested, but also advise the client to submit a sample for standard laboratory testing.
  4. Recommend at-risk clients return for testing at 3 weeks – 6 weeks (lab-based testing) and 3 weeks – 6 weeks – 3 months (POC testing only)

PrEP, PEP and the Window Period

PrEP and PEP Resources