How are HIV and AIDS diagnosed?
A doctor may suspect HIV if symptoms last and no other cause can be found.
If you have been exposed to HIV, your immune system will make antibodies to try to destroy the virus. Doctors use tests to find these HIV antibodies or antigens in urine, saliva, or blood.
A diagnosis of HIV infection is not made until a positive ELISA test is confirmed by a positive test to detect HIV DNA or RNA. A PCR test can do this.
HIV antibodies or antigens usually show up in the blood within 3 months. If you think you have been exposed to HIV but you test negative for it:
- Get tested again. A repeat test may be done after a few weeks to be sure you are not infected.
- Meanwhile, take steps to prevent the spread of the virus, in case you do have it.
- Avoid sexual contact with others. If you do have sex, practice safer sex.
- Do not share needles, syringes, cookers, cotton, cocaine spoons, or eyedroppers.
Getting tested and home test kits
You can get HIV testing in most doctors' offices, public health clinics, hospitals, and Planned Parenthood clinics.
A home test kit for HIV (called OraQuick) has been approved by the U.S. Food and Drug Administration (FDA). For the test, you rub your gums with a swab supplied by the kit. Then you place the swab into a vial of liquid. The test strip on the swab indicates if you have HIV or not.
Another type of test kit for HIV is a home blood test kit. This type of kit provides instructions and materials for collecting a small blood sample by sticking your finger with a lancet. The blood is placed onto a special card that is then sent to a lab for analysis. You get the results over the phone using an anonymous code number. Counseling is also available over the phone for people who use the test kit.
If the results from a home test kit show that you have an HIV infection, talk with a doctor.
Tests after a positive result
If you test positive, your doctor will ask you about your past health and do a physical exam. He or she may order several lab tests to check your overall health, including:
- A complete blood count (CBC), to identify the numbers and types of cells in your blood, especially CD4+ cells.
- A chemistry screen, to measure the blood levels of certain substances (such as electrolytes and glucose) and to see how well your liver and kidneys are working.
Other tests may be done to check for current or past infections that may become worse because of HIV. You may be tested for:
- Syphilis.
- Hepatitis A, hepatitis B, and hepatitis C.
- Tuberculosis (TB).
Ongoing tests
When you have HIV, two tests are done regularly to see how much of the virus is in your blood (viral load) and how the virus is affecting your immune system:
- CD4+ cell counts provide information about the health of your immune system.
- Viral load measures the amount of HIV in your blood.
The results of these tests may help you make decisions about starting treatment or switching to new medicines if the ones you are taking aren't helping.
Tests for drug resistance
HIV often changes or mutates in the body. Sometimes these changes make the virus resistant to certain medicines. Then the medicine no longer works.
Medical experts recommend testing the blood of everyone diagnosed with HIV to look for this drug resistance. This information helps your doctor know what medicines to use.
You also may be tested for drug resistance when:
- You are ready to begin treatment.
- You've been having treatment and your viral load numbers stop going down.
- You've been having treatment and your viral load numbers become detectable after not being detectable.
Tests for AIDS
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. These include Kaposi's sarcoma or Pneumocystis pneumonia.
