General: HIV is diagnosed after HIV antibodies or HIV itself is detected in the patient's body. As soon as the virus enters the body, the immune system produces antibodies, which are proteins that detect foreign substances, such as HIV, that enter the body. The presence of these antibodies in the blood, oral fluid, and urine can be used to determine whether HIV is in the body.

It may take some time for the immune system to produce enough antibodies for the antibody test to detect them. This time period, known as the "window period," varies among patients. Most people will develop detectable antibodies two to eight weeks after exposure, with the average being 25 days. However, some individuals might take longer to develop detectable antibodies. Ninety-seven percent of patients develop antibodies within the first three months following the time of their infection. In very rare cases, it can take up to six months to develop antibodies to HIV. Therefore, if a patient tests negative for HIV in the first three months after possible exposure, repeat testing should be considered longer than three months after the exposure.

In the United States, the test results must remain confidential. Individuals who are younger than 18 years old can consent to or refuse to be tested for HIV, without the involvement of their legal guardians. Test results may not be released to the patient's legal guardian(s) without his/her consent.

Pre-test counseling: According to the U.S. Centers for Disease Control and Prevention's (CDC) new guidelines for HIV testing, HIV prevention counseling is not required to accompany HIV screening. However, the CDC still recommends that patients receive information about HIV infection, transmission, and prevention. Patients should receive information about HIV testing and the meaning of test results. Healthcare providers should also tell the patient when to expect results and that confirmatory testing is necessary if the test result is positive.

Information can be provided to the patient in a face-to-face meeting with a counselor or in a pamphlet, brochure, or video. Patients who are tested with a rapid HIV test should have equal access to the same types of information.

Prevention counseling: Prevention counseling is not mandatory, but it should be offered to all patients when they receive their test results.

Counseling focuses on reducing the risks of HIV infection or transmission. The counselor makes a personalized detailed risk assessment of the patient. The counselor should also suggest behavior changes that may help reduce the patient's risk of developing or transmitting HIV. The counseling session is a chance to clear up any misconceptions or questions the patient has about the disease.

Enzyme-linked immunosorbent assay (ELISA): The most common HIV tests use blood to detect HIV infection. In most cases the enzyme-linked immunosorbent assay (ELISA), tests a patient's blood sample for antibodies. Oral fluid (not saliva), collected from the cheeks and gums, may also be used to perform an ELISA. Oral fluid ELISA tests are considered as sensitive as a blood test. A urine sample may also be used during an ELISA, but this is considered less accurate than a blood or oral fluid test. A positive (reactive) ELISA for all samples must be used with a follow-up (confirmatory) test, such as the Western blot test, to make a positive diagnosis. Although false negative or false positive results are extremely rare, they may occur if the patient has not yet developed antibodies to HIV or if a mistake was made at the laboratory. When used in combination with a Western blot test, ELISA tests are 99.9% accurate.

Western blot test: A Western blot test is typically used to confirm a positive HIV diagnosis. During the test, a small sample of blood is taken and it is used to detect HIV antibodies, not the HIV virus itself. The Western blot test detects specific protein bands that are present HIV patients. When used in combination with an ELISA, the Western blot test is 99.9% accurate.

Polymerase chain reaction (PCR): Polymerase chain reaction (PCR) tests are used to detect HIV's genetic material, called RNA. These tests can be used to screen the donated blood supply and to detect very early infections before antibodies have been developed. This test may be performed just days or weeks after exposure to HIV. Although these tests are the most accurate, they are not performed as often as the other HIV tests because they are expensive and require the skill of a qualified scientist.

Rapid test: A rapid test produces results in about 20 minutes. Rapid tests use a sample of blood or oral fluid to detect HIV antibodies. The patient's sample is placed on a test strip that contains HIV antigens. If the patient has developed HIV antibodies, the strip will change colors, indicating a seropositive result. A positive HIV test should be confirmed with a follow-up confirmatory test before a final diagnosis of infection can be made. These tests have similar accuracy rates as traditional ELISA screening tests.

Home testing kit: Consumer-controlled test kits, popularly known as home testing kits, were first licensed in 1997. The Home Access HIV-1 Test System™ is the only home kit that is approved by the U.S. Food and Drug Administration (FDA). The Home Access HIV-1 Test System™ is available at most local pharmacies. The individual pricks a finger with a special device and places drops of blood on a specially treated card. The card is then mailed to a licensed laboratory for testing. Home testing kits are confidential and patients do not need to provide personal information, such as their name and address, when submitting their samples. Instead, they have a personal identification number (PIN) that is used to call for results. Callers may speak to a counselor before taking the test, while waiting for the test result, and/or after the results are given. All individuals who receive a positive test result are given referrals for a follow-up confirmatory test, as well as information and resources on treatment and support services.

Many patients are asymptomatic (experience no symptoms) when they first become infected with HIV. After one or two months, an estimated 80-90% of HIV patients develop flu-like symptoms, including, headache, fever, fatigue, and enlarged lymph nodes. These symptoms usually disappear after one week to one month and are often mistaken for another viral infection, such as the flu. Despite having minimal or no symptoms during this stage, individuals are very infectious because the virus is present in large quantities in bodily fluids.

The most obvious sign of HIV infection is a decrease in the number of CD4 cells in the blood. These cells help fight against infection. HIV slowly kills these cells without causing symptoms. Even when the infected individual is asymptomatic, the virus is multiplying, infecting, and destroying cells in the immune system.

After the initial infection with HIV, more serious symptoms arise. This next stage of infection is called clinical latency. Once infected with HIV, it may take 10 or more years for more severe symptoms to appear in adults or up to two years in children who are born with HIV infection. The length of this asymptomatic period varies in individuals. Some people may start to experience more serious symptoms within a few months, while others may be symptom-free for several years. The virus can also hide within infected cells and lay dormant. Patients can still transmit the virus to others when the virus is dormant.

As the immune system continues to weaken many symptoms appear, including inflamed lymph nodes (swollen glands) that may be enlarged for longer than three months. Other symptoms often experienced months to years before the onset of AIDS include fatigue, weight loss, frequent fevers and sweats, persistent or frequent yeast infections (oral or vaginal), persistent skin rashes, flaky skin, pelvic inflammatory disease (PID) in women that does not respond well to treatment, and short-term memory loss.

In addition, some individuals develop a painful nerve disease called shingles or frequent and severe herpes infections that cause sores to develop on the mouth, genitals, or anus. Infected children may grow slowly or be sick often.

Once the patient's CD4 T-cell count is less than 200 cells per microliter of blood, their condition has progressed to AIDS, the final stage of the disease. The first symptoms often include moderate and unexplained weight loss, recurring respiratory tract infections, and oral ulcerations.

Patients are vulnerable to opportunistic infections and tumors. Opportunistic infections and tumors may include tuberculosis, thrush, herpes viruses, shingles, Epstein-Barr virus, pneumonia, and a type of cancer called Kaposi's sarcoma (KS). In the last stages of AIDS, it is common for individuals to have cytomegalovirus or Mycobacterium avium complex (MAC) infections.

The U.S. Centers for Disease Control (CDC) recommends that the following individuals get tested for HIV:

Individuals between the ages of 13 and 64 should be tested annually.

Individuals who have injected illegal drugs.

Individuals who have had unprotected vaginal, anal, or oral sex.

Individuals who have multiple or anonymous sexual partners.

Individuals who have exchanged sex for drugs or money.

Individuals who been diagnosed with or treated for hepatitis, tuberculosis (TB), or a sexually transmitted disease (STD), such as syphilis, gonorrhea, or chlamydia.

Individuals who have come in direct contact with an HIV-infected person's blood.

Individuals who had unprotected sex with someone who could answer "yes" to any of the above questions.

Pregnant women should be screened for HIV as part of regular prenatal tests.