Diagnosis
Because
early HIV infection often causes no symptoms, it is primarily detected by
testing a person's blood for the presence of antibodies (disease-fighting
proteins) to HIV. HIV antibodies generally do not reach detectable levels until
one to three months following infection and may take as long as six months to be
generated in quantities large enough to show up in standard blood tests. HIV
testing may also be performed on saliva and urine samples, in addition to blood
samples.
People
exposed to HIV should be tested for HIV infection as soon as they are likely to
develop antibodies to the virus. Such early testing will enable them to receive
appropriate treatment at a time when they are most able to combat HIV and
prevent the emergence of certain opportunistic infections. Early testing also alerts HIV-infected people to avoid high-risk
behaviors that could spread HIV to others.
HIV
testing is done in most doctors' offices or health clinics and should be
accompanied by counseling. Individuals can be tested anonymously at many sites
if they have particular concerns about confidentiality. In addition, blood
samples for anonymous HIV testing may now be collected at home. Home-based test
kits are available by telephone order or over the counter at pharmacies.
Two
different types of antibody tests, ELISA and Western Blot, are used to diagnose
HIV infection. If a person is highly likely to be infected with HIV and yet both
tests are negative, a doctor may test for the presence of HIV itself in the
blood. The person also may be told to repeat antibody testing at a later date,
when antibodies to HIV are more likely to have developed.
Babies
born to mothers infected with HIV may or may not be infected with the virus, but
all carry their mothers' antibodies to HIV for several months. If these babies
lack symptoms, a definitive diagnosis of HIV infection using standard antibody
tests cannot be made until after 15 months of age. By then, babies are unlikely
to still carry their mothers' antibodies and will have produced their own, if
they are infected. New technologies to detect HIV itself are being used to more
accurately determine HIV infection in infants between ages 3 months and 15
months. A number of blood tests are being evaluated to determine if they can
diagnose HIV infection in babies younger than 3 months.
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