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HIV and AIDS
Part 3 - Tecting for HIV
What is the HIV antibody test?
Specific blood tests are used to determine whether there are antibodies to HIV in the blood or not. Detection of HIV antibodies would mean you have been infected with the HIV virus. More than one test may be used to confirm a positive result.
The first test usually done is known as an ELISA test (Enzyme-Linked Immuno-Sorbent Assay.) This test is extremely sensitive, and while it gives very accurate results, it can occasionally give a false positive result. This is why a positive ELISA result will always needs to be confirmed by a second test, called a Western Blot.
When both of these tests are done, a result is considered extremely reliable. A positive ELISA and positive Western Blot test together means that a person is infected with HIV. A negative result on the Western Blot test means that a person does not have HIV even if the result has come back positive on an ELISA test.
What are antibodies?
Antibodies are chemical compounds found in the blood, which are produced by the immune system in response to the presence of a foreign substance, such as an infection. With many infections, the antibodies help the body to recover and fight off infections. With some viruses such as measles, hepatitis A and chicken pox, the antibodies can protect a person from future infection. This is not the case with HIV.
What is the window period? (Or why do I have to wait 12 weeks to test?)
This is the time it takes, following a possible risk of infection with HIV, until a HIV antibody test can give a conclusive result. With the tests that are used for HIV screening in Australia this “window period” is considered to be 12 weeks.
It can take up to 12 weeks for your body to produce these antibodies if you have been infected so testing will be usually be done 12 weeks following the risk . During the window period it is still possible to be infected and to infect others with HIV. It is therefore strongly suggested that condoms be used at all times or that a person abstains from activities that may put them or their partner/s at further risk.
Under certain circumstances it may be possible to get a result before the 12 week window period. However, it is recommended that people wait at least 12 weeks after a risk to ensure result accuracy.
Are there other tests for HIV?
The p24 antigen test looks for the presence of a specific HIV protein. This protein can be found before the appearance of HIV antibodies in a recently infected person. Although this test is useful in certain circumstances it can not be used for confirmation of HIV infection alone. While a positive p24 antigen result means HIV infection, a negative result does not confirm that there is no infection with HIV. Therefore this test is not routinely done when testing for HIV infection but may be used if suspecting a very recent infection when antibody tests are negative and in the 'seroconversion' or 'window period'.
HIV pro-viral DNA PCR testing is not widely available as most laboratories do not have the equipment to run this test. It is sometimes called Nucleic Acid testing (NAT) or PCR testing and is most sensitive test available for confirming the presence of HIV virus. The main use for this test in detecting HIV is in situations when standard testing is inappropriate such as in the diagnosis in newborn infants, pre-seroconversion or where standard testing has been disputed or inconclusive. This test does not replace screening tests or diagnostic testing alone.
ß2-microglobulin testing can be used to see if a HIV infection is recent or not. The test looks for a protein found in blood serum which has been shown to increase the longer a person has had HIV. Elevated concentrations are also found in serum of individuals with advanced HIV infection and in spinal fluid of individuals with AIDS Dementia Complex (ADC), a neurological complication of advanced HIV disease.
HIV RNA or viral load testing is most commonly used to measure the amount of HIV in the blood of someone who is already diagnosed HIV-positive.
What about CD4 testing?
T-cells or CD 4 cells are one of the immune system cells and are destroyed by HIV.
CD4 testing is a common test to look at the strength of the immune system. Although having a low CD4 cell count can indicate immune system damage, it does not necessarily mean that a person has HIV. A HIV test should be taken if there is any concern about HIV. More information on CD4 testing for people who are HIV-positive can be found at the end of this booklet.
What about Rapid HIV Tests?
Rapid tests give same day results but due to a higher number of false positive results two separate tests must be done to confirm a positive result. This means that all potential positive rapid test results cannot be considered confirmatory until standard blood testing is done.
What about Home Test kits?
Home Testing Kits may sound convenient. It involves taking a blood spot or saliva sample at home and then posting it to a laboratory for testing. However, this type of testing may mean that the individual does not receive adequate pre and post-test information, nor counselling and support. The current guidelines for HIV testing in Australia require certain issues to be discussed to enable the individual to make an informed decision regarding testing. At present these test kits are not licensed for use in Australia.
What about Self Test Kits?
A self test kit is defined as one where an individual can administer the test and read the result themselves. Although at present there are self test kits available in some countries, they are not yet licensed nor approved for use in Australia, the United States, United Kingdom or Canada. The accuracy of this test kit is thought to be comparable to that of the rapid testing and home test kits mentioned above.
When should a HIV test be done?
In most cases, it is recommended to wait at least 12 weeks after the possible exposure. This is to allow enough time for HIV antibodies to appear which is what the most commonly run test to detect HIV infection. During this period it is recommended that a person practise safe sex and use condoms to ensure they do not pass HIV on to their partner(s). There may be circumstances when testing earlier than 12 weeks might be considered, eg. due to the presence of specific symptoms, but a conclusive result may still take 12 weeks.
If you are considering testing for HIV, you should also consider testing for other Sexually Transmitted Infections at the same time.
How can I get a HIV test?
Tests are available from your medical practitioner or your nearest Sexual Health Clinic
HIV test results can take up to a week to come back from the laboratory. This is because HIV tests are done in batches and may not be run every day.
Having a HIV test has many implications. Someone should discuss these implications with you as HIV testing should only be done with informed consent (see “What is informed consent” below). For this reason we suggest going to a centre where pre and post-test counselling is carried out.
What is informed consent?
This means you should be able to understand what you are testing for and weigh up the advantages and disadvantages of having a HIV test and assess the potential implications of a positive or negative result. Things to consider are how you would cope with a positive result given your current life circumstances, what supports you would have, and how you have coped with a crisis in the past. It is also necessary under law (in some jurisidictions) that a person diagnosed with HIV must inform current and future sexual partners of the diagnosis before engaging in sex, even if condoms or other methods of protection are used. These things should be discussed with you prior to having a test. The testing procedure will also give information regarding how to potentially prevent HIV infection.
Protection of your privacy
In most jurisidictions, testing and reporting of a HIV result using a person’s full name and address is unlawful except under specific circumstances, such as for insurance or immigration purposes, testing a hospital patient, or when the person being tested has consented to their name being recorded. It is a good idea to ask the centre where you wish to be tested if they use a coding system that does not identify people by personal details.
This information was taken from a booklet created by the NSW HIV/AIDS Information Line |
