quick and easy way to test for HIV antibodies

Enzyme-Linked Immunosorbent Assay (ELISA)

Enzyme-linked immunosorbent assay is a quick and easy way to test for HIV antibodies. The sensitivity (percentage of positive results that are truly positive) and specificity (percentage of negative results that are truly negative) of ELISA approach 100%, but false-positive and false-negative results do occur. A false-negative result is slightly more common, especially in women who have had multiple pregnancies or people who have received multiple blood transfusions.

If the result is positive or indeterminate, the test is repeated. If the second test is positive or indeterminate, a different test, usually the Western blot, is done to confirm the results.

What exactly is an enzyme-linked immunosorbent assay? In this test, the blood sample is added to a slide that is coated with HIV antigens (HIV molecules that trigger an immune system response) and a dye is then added that appears only if HIV antibodies (proteins that the body produces in response to HIV infection) bind with the antigens.

Western Blot

The Western blot is generally used to confirm positive ELISA results, not to screen for infection. It produces more false positive results (i.e., positive tests results that are actually negative) than ELISA.

How does the Western blot work? This test involves putting the blood sample on a strip of paper (made out of nitrocellulose), which is embedded with HIV antigens (HIV molecules that trigger an immune system response). The blood migrates along the paper, and a visible band shows up in places where HIV antibodies (proteins that the body produces in response to HIV infection) bind with the antigens.