For people who think they may have been exposed to HIV, getting tested and receiving a negative result (not infected with HIV), can put their mind at ease.
If the HIV test is positive, there are things that can be done to help a person move on and lead a healthy life.
A person who tests positive will at some point need to take antiretroviral treatment to slow down the virus and maintain a healthy immune system. The longer a person remains unaware of their infection, the less effective the treatment might be. Doctors can monitor a HIV positive person’s health in order to provide the right treatment regimen at the right time.
If a person is aware of their HIV status they can take steps to prevent HIV transmission to other people. They can take treatment, practice safe sex, and inform previous sexual partners that they may have been at risk of infection.
Those who arethinking of starting a family can learn about ways to prevent their child from becoming infected with HIV through mother-to-child transmission.
Where can you be tested for HIV?
HIV testing is provided at a number of locations including:
Specialists such as Advanced Testing Services at testing sites
What does a HIV test involve?
When someone attends a testing site they will speak with a trained counselor prior to the lab visit. They will have a pre-test consultation during which they can ask any questions about the test.
At the lab, the phlebotomist takes a blood sample from the arm . The test is always strictly confidential and only goes ahead if the person agrees to it.
Depending on the test, it can take usually 1 day for the antibody test and 2-4 for PCR results. When the results arrive, the healthcare professional will explain what the results means, and if they are positive, the next course of action regarding treatment.
When should you have a HIV test?
The 'window period' is the term used to describe the period of time between HIV infection and the indicators of HIV infection showing up on tests, such as antibodies and antigens(virus). During this time, a test may give a ‘false negative’ result, which means the test will give a negative result even though a person is infected with HIV. A test must be taken after the window period for an accurate result.
As described below, different types of test have different window periods. A person should always discuss the limitations of the test they are using with a counselor before being tested.
It is very important to note that if a person is infected with HIV, HIV transmission is possible to others during the window period.
Types of HIV tests:
There are a number of tests that are used to find out whether a person is infected with HIV. These include the HIV antibody test, PCR Testing, p24 antigen test and rapid tests. These tests are sometimes used in combination.
1-Antibody tests(Elisa), looks for HIV antibodies. Window - Three months
2-Antigen (p24) test, looks for p24 viral proteins. Window - 11 days to one month. Not as sensitive as PCR.
3- PCR test, looks for genetic material belonging to HIV. Window for RNA PCR - 7 + days. Window for DNA PCR - 11+ days. High sensitivity and reliability.
HIV antibody tests are specifically designed for routine diagnosis of HIV in adults. They are very accurate after 3 months and are sometimes called 'third generation' tests. The ELISA antibody test (enzyme-linked immunoabsorbent) also known as EIA (enzyme immunoassay) was the first HIV antibody test to be widely used.
How do antibody tests work?
When a person is infected with HIV, their body responds by producing special proteins to fight the infection called antibodies. A HIV antibody test looks for these antibodies in blood, saliva or urine. If antibodies to HIV are detected, it means a person has been infected with HIV.
What is the window period for antibody tests?
The window period for a HIV antibody test is estimated to be three months after exposure to HIV infection.
A negative test at three months will almost always mean a person is not infected with HIV.
How accurate are antibody tests?
Antibody tests are extremely accurate in detecting the presence of HIV antibodies. Antibody tests are very sensitive and so will detect very small levels of HIV antibodies. This high level of sensitivity however, means that their specificity (ability to distinguish HIV antibodies from other antibodies) is slightly lowered. As a result, there is a very small chance that a result could come back as ‘false positive’.
A false positive result means that although a person may not be infected with HIV, their antibody test comes back positive. All positive test results are followed up with a confirmatory test, such as:
A Western blot assay – one of the oldest but most accurate antibody tests. It should only be used to confirm a repeatedly reactive Elisa test.
A PCR test (Polymerase Chain Reaction test) detects the genetic material of HIV in the blood. It can identify HIV in the blood within one to two weeks of infection. There are two tests. The viral load test or RNA PCR and the DNA PCR.
Babies born to HIV-positive mothers are typically tested using a PCR test because they retain their mother's antibodies for several months, making an antibody test inaccurate. Blood supplies in most developed countries are screened for HIV using PCR tests. In the United States, PCR tests have been used to screen blood donations since 2001 as they shorten the window perod.
What is the window period for a PCR test?
The window period for a PCR test is estimated to be 7-11 days after exposure to HIV infection.