HIV/Aids

Updated 04 January 2018

Diagnosing HIV/Aids

Find information on diagnostic testing for HIV/Aids, when to get tested and how the testing procedure pinpoints a positive or negative result.

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If you think you may have been exposed to HIV, it’s important to get tested. Testing is the only way to know for sure whether you have HIV – and knowing your status means you can keep yourself and others healthy. 

After contracting HIV, most people develop antibodies – cells that fight infection in the body. These antibodies can usually be detected through blood and/or saliva tests within three months of infection (the average time of successful detection is 25 days after exposure to HIV).

Testing technology has improved substantially over the last few years. Previously, tests only detected the presence of antibodies. Now, fourth-generation antigen/antibody tests are being used more frequently, making it possible to detect the virus much faster and more accurately.

Your clinic nurse or doctor will most likely perform a saliva or blood test (a sample of blood will be taken from your finger or arm). 

ELISA antibody/antigen test

Until a couple of years ago, the most widely used antibody test was the third-generation ELISA (enzyme linked immunoassay) test. With this test, you had to wait a couple of days to get your test results (which, for many patients, caused a great deal of stress and anxiety).

These days, most laboratories screen with the fourth-generation ELISA test. This test detects antibodies as well as a viral protein called p24 antigen, which forms part of the virus itself. The p24 antigen appears in the blood a week before the antibodies, which shortens the window period – the period between potential exposure to HIV infection and an accurate test result.

If a positive result is obtained on an ELISA test, the laboratory will confirm the result by testing with at least one other type of test. As an additional check, a second blood specimen is usually taken for repeat testing.

Rapid HIV tests

Rapid tests have become popular in Africa, as they’re highly reliable (over 99% accurate) and cost effective. The result is also available within 20 - 30 minutes. False positives rarely occur – if they do, it’s a result of antibodies that cross-reacted in the testing system. False negative tests can also occur, especially if the test is done too soon after exposure to HIV (i.e. when you’re still in the window period).

Testing can be done by any healthcare professional at a clinic, hospital or private practice. Either a small sample of blood (from a prick on the finger) or a sample of mucous is taken from the inside of your cheek or gums. If the test is positive, a second test will be done immediately, either using a different rapid test or an ELISA (enzyme linked immunoassay) test. Both tests must be positive to confirm a diagnosis of HIV.

HIV self-testing kits

Home HIV tests are currently also available through some South African pharmacies. The World Health Organization (WHO) encourages home testing, as it offers a way for many more people to learn their HIV status. Worldwide, an estimated 40% of all people with HIV still remain unaware of their status.

Most HIV self-testing kits are simple to use, require a sample of blood from a finger prick, and can give you results within 15 minutes. Note that if your HIV home test indicates that you’re HIV positive, you should confirm the diagnosis with a second test at your doctor, hospital or clinic. You can also call the National AIDS Helpline on 0800 012 322 for counselling and advice.

HIV PCR test for babies

In babies younger than 18 months, the mother's antibodies can interfere with the HIV antibody test. These antibodies may still be present in the baby’s blood. To test accurately whether a baby is HIV-positive, the virus itself must be detected (not the antibodies). This can be done with a polymerase chain reaction (PCR) test.

In South Africa, this test is routinely used for all babies of HIV-infected mothers at six weeks. Infants who are found to be PCR-positive are immediately referred for antiretroviral treatment (ART).

A note on the window period

In rare cases, it can take up to six months to be able to detect HIV antibodies. Because of this, you should get tested three months after your most recent possible exposure to HIV. If your test comes back negative, it should be repeated three months later, in case you’re still in the window period.

Where to get tested
There are many places that offer private and confidential testing for HIV, both within the public and the private sector in South Africa. This includes:

  • Doctors’ rooms
  • Hospitals
  • Community health centres
  • Family-planning clinics
  • Clinics that specialise in sexually transmitted infections
  • Laboratories   

Most of these places provide free HIV testing. Make sure that, wherever you get tested, pre- and post-test counselling is available. This will help you to deal with the psychological stress and anxiety that you’re likely to experience while waiting for your results and if you get a positive result. Remember that you can also call the National AIDS Helpline on 0800 012 322 for counselling and advice.

Avoid sexual contact with others while waiting for your test results.

Should you get tested for HIV

You should get an HIV test if you’ve engaged in behaviour that puts you at risk of contracting the virus (see ‘What causes HIV/AIDS?’). High-risk behaviour includes having unprotected sex and using intravenous drugs with unsterilised needles.

The benefits of getting tested:

  • The sooner you get tested, the sooner you can access treatment and information to help keep your immune system healthy, manage the virus and delay the onset of AIDS (if you’re HIV-positive).
  • Knowing your status means you can make an extra effort to stay as healthy as possible. You’ll have to adopt a healthy, nutritious diet, exercise regularly, sleep and rest enough, and avoid cigarettes and alcohol.
  • If you know you’re HIV-positive, you can protect your partner from becoming infected. If more people know their HIV status and use the knowledge to act responsibly, the pandemic can be better controlled.
  • If you’re pregnant and test HIV-positive, appropriate treatment can reduce the risk of your baby becoming infected too.
  • Finding out your HIV status as early as possible gives you time, if you’re infected, to make plans for yourself and your dependents to be looked after when you get sick.
  • You can help educate others about HIV/AIDS, and improve their attitudes and behaviours relating to the disease. Consider talking about your HIV status and your decision to get tested, but remember that sharing this information is entirely your decision. The health professionals and counsellors who conduct and discuss the test with you must, by law, keep the results strictly confidential.

Note that diagnostic testing for HIV can only be done with your consent. Pre-employment testing is illegal in South Africa. Although testing by life insurance companies is still often required, it can only be done with your consent. 


 

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Ask the Expert

HIV/Aids expert

Dr Sindisiwe van Zyl qualified at the University of Pretoria in 2005. She is a patients' rights activist and loves using social media to teach about HIV. She is in private practice in Johannesburg.

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