Your doctor will ask about possible HIV risk factors, such as previous sexual partners, intravenous drug use, blood transfusion and occupational exposure to blood, such as accidentally being stuck by needles. Your doctor might ask about a variety of symptoms, such as fever, weight loss, muscle and joint aches, fatigue and headache, and about medical problems you may have had in the past like sexually transmitted infections or hepatitis.
This typically is followed by a complete physical examination. During the exam, your doctor will look for a thick, white coating on your tongue called thrush (infection with Candida), any skin abnormalities and swollen lymph nodes. To make the diagnosis of HIV infection, however, laboratory tests are needed.
HIV testing can be done with a blood test done in your doctor's office or in an anonymous clinic. In some places, the test can be done with an oral swab and uses saliva instead of blood.
The initial screening test is called an enzyme immunoassay (EIA or sometimes an enzyme linked immunosorbent assay [ELISA]). The EIA detects disease-fighting proteins that are made by your immune system called antibodies: The EIA test for HIV infection looks for antibodies made by your immune system specifically against the virus.
If the EIA is positive, a Western blot test, which also measures the body's antibody response to HIV but is more accurate than the EIA, is done to confirm the diagnosis. There are several causes of false positive EIAs, but a false positive Western blot is very rare.
Neither the EIA nor the Western blot is accurate immediately after a person is infected with the HIV virus. It can take a few months for these tests to become positive. The period between infection with HIV and the development of positive test for antibodies is called "the window period." This term refers to the window of time between getting the HIV infection and the ability to detect the body's response to infection (the development of antibodies).
To diagnose people with acute HIV or those that may be in the window period, a viral load blood test is needed.
If you have been diagnosed with HIV by an antibody test, your doctor will order additional tests including a viral load and CD4 cell count.