Human Immunodeficiency Virus (HIV) Infection - Exams and Tests

Exams and Tests

Getting tested for HIV can be scary, but the condition is treatable so it is important to get tested if you think you have been exposed. If you test positive, early detection and monitoring of HIV will help your doctor determine whether the disease is progressing and when to start treatment.

Your doctor may recommend counseling before and after HIV testing, and it is usually available at the hospital or clinic where you will be tested. This will give you an opportunity to:

• Discuss your fears about being tested.
• Learn how to reduce your risk of becoming infected if your test is negative.
• Learn how to keep from spreading HIV to others if your test is positive.
• Think about personal issues, such as how having HIV will affect you socially, emotionally, professionally, and financially.
• Learn what you need to do to stay healthy as long as possible.

HIV is diagnosed when antibodies to HIV are detected in the blood. The two primary blood tests used to detect the HIV antibodies are:

• Enzyme-linked immunosorbent assay (ELISA).
• Western blot assay, used to confirm the results of a positive ELISA test.

HIV is diagnosed only after two or more positive ELISA tests are confirmed by one positive Western blot assay.

It can take as little as 2 weeks or as long as 6 months from the time you become infected with HIV for the antibodies to be detected in your blood. This is commonly called the "window period," or seroconversion period. During the window period, you are contagious and can spread the virus to others. If you think you have been exposed to HIV but you test negative for it, you should be tested again 6 months later.

Testing positive for HIV infection

Testing positive for HIV will probably make you anxious and afraid about your future. The good news is that people being treated for HIV are living longer than ever before with the help of medicines that slow the rate at which HIV progresses to AIDS. Your doctor can help you understand your condition and how best to treat it.

If you test positive for HIV, your doctor will complete a medical history and physical examination. He or she may order several lab tests to evaluate your overall health condition and identify current or previous infections that may become more complicated because of HIV. These tests include:

• A complete blood count (CBC), to identify the numbers and types of cells in your blood.
• A chemistry screen, to measure the blood levels of certain substances (such as electrolytes and glucose) and to evaluate liver and kidney function.
• Syphilis testing.
• Screening for hepatitis A, hepatitis B, and hepatitis C, to test for past or current infection with viruses that cause hepatitis.
• Tuberculosis (TB) screening, to detect bacteria that cause tuberculosis.
• A chest X-ray, to detect lung problems associated with HIV.
• Toxoplasmosis testing, to detect the parasite that causes toxoplasmosis (an infection caused by eating undercooked meats or contact with some animals such as cats). This condition can become serious in people who have weakened immune systems.

Some strains of HIV may be resistant to certain medicines. If you tested positive for HIV, your doctor may test you at this stage to see if you have been infected with a drug-resistant strain of HIV. This will help him or her determine which medicines to use to treat the infection.

Your doctor will use the results of the physical exam and lab tests to determine the progression of HIV at later exams.

What to think about

The Centers for Disease Control and Prevention (CDC) recommend HIV screening as part of routine blood testing. You and your doctor can decide if testing is right for you.

Most test facilities will have the ELISA test results in 2 to 4 days. Results of the Western blot take longer—1 to 2 weeks. The OraQuick Rapid HIV-1 Antibody test gives results in as little as 20 minutes. Although the OraQuick test is known to be very accurate, recently there have been more test results that appear to show HIV when in fact HIV is not present (false-positive). Experts are not sure why this is happening.

Call and ask for your HIV test results if you have not been contacted within 1 to 2 weeks of being tested.

Denial, fear, and depression are common reactions to a diagnosis of HIV. Don't be afraid to ask for the emotional support you need. If your family and friends are unable to provide you with support, a professional counselor can help.

Monitoring of established HIV infection

Two tests will be done regularly to monitor how much HIV is in your blood (viral load), and how the virus is affecting your immune system. The results of these tests will help you make decisions about starting highly active antiretroviral therapy (HAART) or switching to new medicines if the ones you are currently taking are not effective.

• CD4+ cell counts provide information about the health of your immune system.
• Viral load measures the amount of HIV in your blood.

Testing for drug resistance

HIV often changes or mutates in the body. Sometimes these changes make the virus resistant to a particular medicine or class of medicines. This means the medicine can no longer slow down or prevent the virus from multiplying or protect the immune system.

Two blood tests are available to detect drug resistance in the virus:

• Genotyping assays, which detect mutations in the viral genes. Test results are generally available in 1 to 2 weeks.
• Phenotyping assays, which measure the ability of the virus to grow in cells with antiretroviral medicines. Test results are generally available in 2 to 3 weeks.

You may be tested for drug resistance when you first test positive for HIV, HIV symptoms reappear, viral load numbers stop declining, or viral load numbers become detectable after not being detectable while on treatment.

Drug resistance can occur when:

• There is a change in the way your body absorbs the medicine.
• There are interactions between two or more medicines you are taking.
• The virus changes and no longer responds to the medicines you are taking.
• You have been infected with a drug-resistant strain of the virus.
• You have not taken your medicines as prescribed by your doctor.

Other medicines are available that may treat some resistant strains of HIV.

How is AIDS diagnosed?

AIDS is the last and most severe stage of HIV infection. It is diagnosed if the results of your test show that you have:

• A CD4+ cell count of less than 200 cells per microliter (mcL) of blood.
• A certain kind of infection called an opportunistic infection that is common in people who have weakened immune systems, such as Kaposi's sarcoma or Pneumocystispneumonia.

Early Detection

The United States Preventive Services Task Force (USPSTF) recommends screening tests for HIV if:

• You or your sex partner(s) engage in high-risk behavior.
• You are pregnant. Early treatment with highly active antiretroviral therapy (HAART) can reduce the risk of passing HIV to your baby.