How the Test is Performed
A blood sample is needed. For information on how this is done, see: Venipuncture.
How to Prepare for the Test
No preparation is necessary.
How the Test Will Feel
When
the needle is inserted to draw blood, some people feel moderate pain,
while others feel only a prick or stinging sensation. Afterward, there
may be some throbbing.
Why the Test is Performed
Testing for HIV infection is done for many reasons, including:
- Screening people who want to be tested
- Screening
people in high-risk groups (men who have sex with men, injection drug
users and their sexual partners, and commercial sex workers)
- Screening people with certain conditions and infections (such as Kaposi's sarcoma or Pneumocystis jirovecii pneumonia)
- Screening pregnant women to help prevent them from passing the virus to the baby
- When a patient has an unusual infection
Normal Results
A
negative test result is normal. However, people with early HIV
infection (termed acute HIV infection or primary HIV infection) often
have a negative test result.
What Abnormal Results Mean
A positive result on the ELISA
screening test does not necessarily mean that the person has HIV
infection. Certain conditions may lead to a false positive result, such
as Lyme disease, syphilis, and lupus.
A
positive ELISA test is always followed by a Western blot test. A
positive Western blot confirms an HIV infection. A negative Western blot
test means the ELISA test was a false positive test. The Western blot
test can also be unclear, in which case more testing is done.
Negative
tests do not rule out HIV infection. There is a period of time (called
the "window period") between HIV infection and the appearance of
anti-HIV antibodies that can be measured.
If
a person might have acute or primary HIV infection, and is in the
"window period," a negative HIV ELISA and Western blot will not rule out
HIV infection. More tests for HIV will need to be done.
Risks
Veins
and arteries vary in size from one patient to another and from one side
of the body to the other. Obtaining a blood sample from some people may
be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Considerations
People
who are at high risk (men who have sex with men, injection drug users
and their sexual partners, commercial sex workers) should be regularly
tested for HIV.
If the health care provider suspects early acute
HIV infection, other tests (such as HIV viral load) will be needed to
confirm this diagnosis, because the HIV ELISA/Western blot test will
often be negative during this window period.
Alternative Names
HIV testing
