HIV 1 & 2 ANTIBODIES

This HIV test is 99.8% accurate from 12 weeks post exposure.

A HIV Proviral Test is 99.9% accurate from 10 days post exposure

Various laboratory methods are available to screen blood, diagnose infection, and monitor disease progression in individuals infected by HIV.

Screening tests possess a high degree of sensitivity, whereas confirmatory assays have a high specificity. Tests with high sensitivity may produce few false-positive results, whereas tests with high specificity produce few false-negative results. These classes of assays, performed in tandem, produce results that are highly accurate, reliable, and assist in the diagnosis of HIV.

Specific HIV antibodies are produced shortly after infection. The time depends on several factors, including host and viral characteristics. Antibodies may also be present at low levels during early infection but not at the detection limit of some assays.

New fourth generation antigen sandwich assays can detect HIV antibodies from about 4 weeks post exposure. This HIV 1 & 2 Antibody + p24 Antigen test is a double-antigen sandwich combination assay called the Elecsys-HIV Combi that has been reported to have a specificity of 99.8%.

The antigen sandwich method is when an enzyme (alkaline phosphatase or horseradish peroxidase) is conjugated to an HIV antigen. The antibody in the sample is "sandwiched" between two antigen molecules, one immobilized on the solid phase and one containing the enzyme.

Subsequently, the addition of substrate results in colour development in proportion to antibody concentration. The antigen sandwich ELISA is considered the most sensitive screening method, given its ability to detect all isotypes of antibody (including IgM).

The window period before the detection of antibodies can be shortened by several days using combined antibody and antigen tests, and by several more days using PCR DNA / RNA methods.

During acute HIV infection, prior to the appearance of antibody (window period or pre-seroconversion), HIV infection can only be confirmed by the demonstration of circulating p24 antigen, or the presence of viral RNA or DNA. Although highly sensitive antibody assays exist to detect very low levels of HIV antibody in blood, the window period prior to appearance of antibody can rarely be shortened to less than 3 weeks.

Once antibody has appeared, titres progressively increase during 3-5 months until levels peak, at which time they remain fairly constant throughout the remainder of infection.