Screening Tests for HIV Diagnosis and Treatment

If you're worried that you might have been exposed to human immunodeficiency virus ( HIV),  the virus that causes AIDS - it's important to get tested as soon as possible. Although the prospect of being diagnosed with the disease can be scary, today you can live a long and full life with HIV, especially if you start treatment early. Knowing you are infected can also help you take precautions so that you don't pass the virus to other people.

Several different tests are used to diagnose HIV infection. Other tests are used to select and monitor treatments in people who are living with HIV. This article covers both types of HIV tests.

You are at risk for HIV infection and should be tested for it if:
    You’ve had several sexual partners.
    You had unprotected sex with someone who is or could be HIV-positive.
    You have used injected drugs or steroids or shared needles or other equipment during drug use.
    You have had any sexually transmitted disease, including herpes, hepatitis, or TB.
    You have had sex for drugs or money.
    You’ve had sex with someone who has a history of any of the above - or with someone whose sexual history you don’t know.

There are several types of tests that screen blood (and sometimes saliva)  to see if you are infected with HIV.

Newer tests can detect the presence of HIV antigen, a protein, up to 20 days earlier than standard tests. This helps prevent spread of the virus to others and means an earlier start for treatment. It is done with a pinprick to the finger.

Here's a look at available HIV tests:

Standard tests. These blood tests check for HIV antibodies. Your body makes antibodies in response to the HIV infection. These tests can't detect HIV in the blood soon after infection because it takes time for your body to make these antibodies. It generally takes two to 8 weeks for your body to produce antibodies, but in some cases it can take up to six months.

In standard tests, a small sample of your blood is drawn and sent to a lab for testing. Some of the standard tests use urine or fluids that are collected from the mouth to screen for antibodies.

Rapid antibody tests. Most of these are blood tests for HIV antibodies. Some can detect antibodies in saliva. Results are available in under 30 minutes and are as accurate as standard tests.

Antibody/antigen tests. These tests are recommended by the CDC and can detect HIV up to 20 days earlier than standard tests. They check for HIV antigen, a part of the virus that shows up 2-4 weeks after infection. These tests can also detect HIV antibodies. A positive result for the antigen allows treatment to begin earlier and the patient to avoid infecting others. These are blood tests only.
 Rapid antibody/antigen test. One antibody/antigen tests delivers results in 20 minutes.

In-home test kits. These kits there are two available in the U.S. screen blood and saliva for HIV antibodies. You can buy them at your local store. The Home Access HIV-1 Test System requires a small blood sample that is collected at home and sent to a lab. The user, who may remain anonymous, can get results by phone in three business days. The Ora Quick In-Home HIV Test can detect HIV antibodies in saliva, if the antibodies are present (which can take up to 6 months). The user swabs the upper and lower gums of their mouths, places the sample in a developer vial, and can get results in 20-40 minutes. A follow-up test should be done if the result is positive.

HIV Screening Tests After Diagnosis:

While being treated for HIV, your doctor will perform several tests to monitor your health, determine when you need to start treatment, and check how well treatment is working. These include:

CD4 count. CD4 is a protein that lives on the surface of infection-fighting white blood cells called T-helper cells. HIV targets these immune cells.

To monitor the health of your immune system, your doctor will check your CD4 count -- the number of CD4 cells in a sample of blood. You should have your CD4 count tested every three to six months during treatment.

A normal CD4 count is more than 500 cells per cubic millimeter (mm3) of blood. The lower the CD4 count, the less your immune system is functioning, and the more likely you are to get infections. Your doctor will probably start treatment by the time a CD4 count is under 500 cells/mm3. If your CD4 count drops to below 200/mm3, you are said to have full-blown AIDS.

Viral load test. A viral load test measures how much of the HIV virus is in the blood. You want to have a low viral load because it means treatment is helping to control the virus. If your treatment is working effectively, the viral load should drop to an undetectable level in your blood.

You'll have your viral load tested two to four weeks after starting treatment, then every four to eight weeks until the viral load is no longer detectable. An undetectable viral load doesn't mean you're not infected just that the amount of HIV in the blood is too low for the test to pick up.