Human Immunodeficiency Virus (HIV) Test

A human immunodeficiency virus (HIV) test detects antibodies to HIV in the blood. This determines whether an HIV infection is present (HIV-positive). HIV infects white blood cells called CD4+ cells, which are part of the body's immune system that help fight infections. HIV causes acquired immunodeficiency syndrome (AIDS), a long-term chronic disease that cannot be cured.

After the original infection, it takes between 2 weeks and 6 months for antibodies to HIV to appear in the blood. The period between becoming infected with HIV and the point at which antibodies to HIV can be detected in the blood is called the seroconversion or "window" period. During this period, an HIV-infected person can still spread the disease, even though a test will not detect any antibodies in his or her blood.

Several tests can find antibodies or genetic material (RNA) to the HIV virus. These tests include:

• Enzyme-linked immunosorbent assay (ELISA). This test is usually the first one used to detect infection with HIV. If antibodies to HIV are present (positive), the test is usually repeated to confirm the diagnosis. If ELISA is negative, other tests are not usually needed. This test has a low chance of having a false result after the first few weeks that a person is infected.
• Western blot. This test is more difficult than the ELISA to perform, but it is done to confirm the results of two positive ELISA tests.
• Polymerase chain reaction (PCR). This test finds either the genetic material RNA of HIV. PCR testing is not done as frequently as antibody testing because it requires technical skill and expensive equipment. This test may be done in the days or weeks after exposure to the virus. Genetic material may be found even if other tests are negative for the virus. The PCR test is very useful to find a very recent infection, determine if an HIV infection is present when antibody test results were uncertain, and screen blood or organs for HIV before donation.
• Indirect fluorescent antibody (IFA). This test detects HIV antibodies. Like a Western blot test, it is used to confirm the results of an ELISA. However, it is more expensive than a Western blot test and not commonly used.

Testing is often done at 6 weeks, 3 months, and 6 months after exposure to find out if a person is infected with HIV.

A test for the human immunodeficiency virus (HIV) is done to:

• Detect an HIV infection. Testing is often done for people with risk factors for HIV infection and people who have symptoms of an HIV infection.
• Screen blood, blood products, and organ donors, to prevent the spread of HIV.
• Screen pregnant women for HIV infection. The United States Preventive Services Task Force recommends all pregnant women be screened. Pregnant women who are infected with HIV and receive treatment are less likely to pass the infection on to their babies than are women who do not receive treatment.

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.

This test is not done to determine if a person has AIDS. A diagnosis of AIDS means a person is HIV-positive and other problems are present.

No special preparation is needed before having this test.

A test for HIV infection cannot be done without your consent. Most health professionals offer counseling before and after the test to discuss:

• How the test is done, what the results mean, and any other tests that may be done.
• How the diagnosis of an HIV infection may affect your social, emotional, professional, and financial outlooks.
• The benefits of early diagnosis and treatment.

Before the test, it is important to tell your health professional how and where to contact you when your test results are ready. If your health professional has not contacted you within 1 to 2 weeks of your test, call and ask for your results.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Apply a gauze pad or cotton ball over the needle site as the needle is removed.
• Apply pressure to the site and then a bandage.

You may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. However, many people do not feel any pain (or have only minor discomfort) once the needle is positioned in the vein. The amount of pain you feel depends on the skill of the health professional drawing the blood, the condition of your veins, and your sensitivity to pain.

There is very little risk of complications from having blood drawn from a vein.

• You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.
• Rarely, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.
• Continued bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medications can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medication, tell your health professional before your blood is drawn.

A human immunodeficiency virus (HIV) test detects antibodies to HIV in the blood. This determines whether an HIV infection is present (HIV-positive). ELISA results are usually available in 2 to 4 days. Results of the other tests, such as the Western blot or IFA, take 1 to 2 weeks.

Factors that can interfere with your test or the accuracy of the results include:

• The use of corticosteroids.
• Antibody testing during the seroconversion period.
• Having an autoimmune disease, leukemia, or syphilis.
• Drinking too much alcohol.

• After initial testing, it is important for your health professional to contact you with the results of your test. Be sure to tell your health professional how and where to contact you. If your health professional has not contacted you within 1 to 2 weeks of your test, call and ask for your results.
• The ELISA is a good screening test because it is usually positive when an HIV infection is present. However, the ELISA test results can indicate HIV is present when it is not (false-positive). Therefore, the ELISA alone cannot be used to make a definite diagnosis of HIV infection.
• Detecting HIV in a newborn infant is difficult. Until about 18 months of age, even a baby who is not infected may still have HIV antibodies received from his or her HIV-positive mother.
• To be certain that an HIV infection is not present, a person must test negative for the virus at least 6 months after the last possible exposure to HIV. Testing is often done at 6 weeks, 3 months, and 6 months to find out whether a person is infected.
• Home blood test kits to detect an HIV infection are available without a prescription at pharmacies or through mail order. These kits provide instructions and materials for collecting a blood sample that is then sent to a lab for analysis. Results are available over the phone using an anonymous code number. Counseling is also available over the phone for people who use the test kit. Rapid test kits are also available and results are received within a half-hour, compared to 1 to 2 weeks with conventional testing. Positive rapid HIV test results need to be confirmed by a Western blot test.
• A screening test for HIV infection may also be done on urine or saliva. An oral HIV test finds antibodies to HIV. Urine testing is rarely done.
• Oral test kits that find HIV-1 and HIV-2 in saliva have been approved by the United States Food and Drug Administration (FDA). The test results are provided the same day. Test results that indicate an HIV infection need to be confirmed by a Western blot test.
• Most states require health professionals, clinics, and hospitals to report confirmed cases of HIV infection to the state health department. Some states allow anonymous reporting (the person's name or other identifying information is not provided). Other states require confidential reporting (identifying information is provided, but only to authorized public health officials). All states must report the numbers of cases of AIDS, without names or other identifying information, to the Centers for Disease Control and Prevention (CDC).
• If you have a positive test result, contact your sex partners to inform them. They may want to be tested. You may be able to get help from your local health department to do this.
• Once an HIV infection is present, other tests are done to determine when to treat the infection and how treatment is working. These tests include a CD4+ count and the viral load. For more information, see the medical tests CD4+ Count and Viral Load Measurement.
• Two types of HIV have been identified.
  • HIV-1 causes almost all of the cases of AIDS worldwide.
  • HIV-2 is found mostly in West Africa.

Other Works Consulted

• Agency for Healthcare Research and Quality (2005). Screening for Human Immunodeficiency Virus Infection (AHRQ Publication No. 05-0580-A). Rockville, MD: Agency for Healthcare Research and Quality. Also available online: http://www.ahrq.gov/clinic/uspstf/uspshivi.htm.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.