Summary

• HIV serology testing measures HIV antibodies in your blood to see whether you are infected with the human immunodeficiency virus.
• All positive HIV serology test results must be confirmed using a Western Blot test.
• The only reliable way to tell if you are infected with HIV is to be tested.

What is HIV?

HIV (Human immunodeficiency virus) is a virus that affects your immune system. It damages a type of immune cell called CD4 cells (also known as T-helper cells). These cells help your body stay healthy by fighting off disease. They identify, attack and destroy bacteria, fungi and other viruses that infect the body.

HIV kills CD4 cells. The number of CD4 cells gradually declines as the HIV disease progresses and if left untreated, this can lead to AIDS (acquired immunodeficiency syndrome) within about 10 years. Over time, common viruses and bacteria that are not dangerous to healthy people can cause repeated infections in someone with AIDS and as their immune system weakens they become less able to stop certain cancers from developing.
The only reliable way to tell if you are infected with HIV is to be tested. This is because you may have no symptoms, or they may be mild and similar to other illnesses, such as flu.

By identifying HIV through blood tests, antiretroviral therapy (ART) can be started. ART is a combination of medicines taken together to stop the virus from reproducing in your body. This is a very effective treatment, and it enables people with HIV to live long and healthy lives and greatly reduce the risk of passing the virus to other people.

There are several different types of tests used to diagnose and manage HIV including HIV serology or antibody tests, HIV genotypic resistance testing (used to identify gene mutations in the HIV virus that cause resistance to antiretroviral drugs) and HIV viral load (the number of copies of virus in your blood).

Why get tested?

There are two types of HIV, HIV-1 and HIV-2. HIV-2 is rare in Australia and more common in West Africa. HIV serology tests detect antibodies to both HIV-1 and HIV-2 in a sample of blood. Newer serology testing also detects HIV P24 antigen, a protein on the surface of the virus.
HIV can be spread in various ways and so testing may be requested if you:

• Have had multiple sexual partners or sex with a person known or suspected to have a HIV infection.
• Received a blood transfusion before 1985, or a sexual partner received a transfusion and later tested positive for HIV. (Since 1985, all blood donated in Australia, the UK and the US is tested for HIV, and infection by transfusion is highly unusual.)
• Are a male who has had sex with another male.
• Have used street drugs by injection, especially when sharing needles and/or other equipment.
• Have a sexually transmitted disease (STD).
• Are a health care worker with direct exposure to blood at work.
• Are pregnant or planning a pregnancy. (There are now treatments that can greatly reduce the risk of passing on the virus to the baby.)
• Are diagnosed with another infection or recurrent infections that may have an association with HIV.
• Undergoing investigation for other medical conditions.

Testing
HIV serology or antibody testing is used to decide whether or not you have been infected by HIV. The test measures the amount of HIV antibodies that your body produces as a response to the virus.

Your immune system protects you by making antibodies to attack substances that are foreign to your body and could be harmful to you. This includes infections like viruses and bacteria as well as substances that could be toxic.

In the initial phase of the infection, also called the acute phase, p24 antigen particles (a protein that is part of the virus) can be found in the blood. When you're first infected with HIV, and before your body has a chance to make antibodies to the virus, your blood has a high level of p24.

P24 can be detected by the HIV P24 antigen test. However, p24 antigen is only detectable during a short window of time which means the test is less reliable if you have been infected for some weeks.

Antibodies to HIV do not appear until about 20 days after the infection and may take up to three months to appear in the blood. This means that if you are tested with an antibody test too soon after the initial infection, the test result may be negative. Because of this, repeat testing is important, for up to six months from the time when you may have been exposed to the virus.

If your result is positive, another blood sample will be collected, and a further test called a Western Blot will be carried out to confirm if you are positive.

If a diagnosis is confirmed, further tests may be requested such as HIV Viral Load, HIV Genotypic Resistance and CD4 cells as part of future management and therapy. Other testing to rule out potential co-infections will also be undertaken.

In Australia, the HIV test is free and anonymous. You can be tested by your doctor, at any sexual health clinic or special clinic for HIV screening. Your doctor is not informed of the result without your permission.

Your medical team will give you advice about informing sexual partners if your test result is positive.

You must have a test if you want to become a blood donor, use your sperm for artificial insemination, have an egg implantation or adopt a child.

Having the test

Sample

Blood

Any preparation?

None

Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

If you have a positive HIV antibody test, which is confirmed by a positive Western Blot test, you will be considered as being infected with HIV. Occasionally, there are false positive results with the antibody test, but it is very unusual to get false positives results with the Western Blot test.

The Western Blot test detects only HIV-1 so if you are infected with HIV-2 (very unusual in Australia) a more specific test will have to be performed.

If your test result is negative, it may be because you have been tested too soon after the initial infection and repeat testing may be needed.

Any more to know?

If your test is positive for HIV, it is wise to tell your healthcare providers and important that you tell all sex partners and/or anyone with whom you share needles. Your doctor should discuss your legal responsibilities relating to disclosure.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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