HIV AIDS screening

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editors-in-Chief: Ujjwal Rastogi, MBBS [2]

Overview

About 1 million Americans have HIV — to a surprise, an estimated 25 percent do not know they have the infection. Therefore, HIV screening is important to both extend their lives and prevent further spreading of the disease.

Screening

HIV can be transmitted to a person receiving blood or organs from an infected donor. To reduce this risk, blood banks and organ donor programs screen donors, blood, and tissues thoroughly. People who received blood transfusions or clotting products between 1977 and 1985 (before screening for the virus became standard practice) are at highest risk for getting HIV. Basic screening lab tests and regular cervical Pap smears are important to monitor in HIV infection, due to the increased risk of cervical cancer in women with a compromised immune system.

Screening donor blood and cellular products

Tests selected to screen donor blood and tissue must provide a high degree of confidence that HIV will be detected if present (that is, a high sensitivity is required). A combination of antibody, antigen and nucleic acid tests are used by blood banks in Western countries. The World Health Organization estimated that, inadequate blood screening had resulted in 1 million new HIV infections worldwide.

In the USA, since 1985, all blood donations are screened with an ELISA test for HIV-1 and HIV-2, as well as a nucleic acid test. These diagnostic tests are combined with careful donor selection. The risk of transfusion-acquired HIV in the U.S. was approximately one in 2.5 million for each transfusion.

Diagnosis of HIV infection

Tests used for the diagnosis of HIV infection in a particular person require a high degree of both sensitivity and specificity. In the United States, this is achieved using an algorithm combining two tests for HIV antibodies. If antibodies are detected by an initial test based on the ELISA method, then a second test using the Western blot procedure determines the size of the antigens in the test kit binding to the antibodies. The combination of these two methods is highly accurate (see below).