Enzyme-Linked Immunosorbent Assay (ELISA)
The most common HIV tests use blood to detect HIV infection. 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 the confirmatory Western blot test, ELISA tests are 99.9% accurate.
