Aviditetstest

Aviditetstest, also known as an avidity test, is a serological assay that measures the overall strength of binding between antibodies and their antigens, an attribute known as antibody avidity. Avidity increases as the immune response matures, so these tests can help distinguish recent from past infections in certain diseases.

Principle and method: The assay typically involves exposing antigen-antibody complexes to a chaotropic agent (such as urea or ammonium thiocyanate) that disrupts weaker, low-avidity interactions. The amount of antibody that remains bound is then measured, usually by an immunoassay such as ELISA or immunoblot. The result is expressed as an avidity index, often calculated as the ratio of the signal after chaotropic treatment to the signal without treatment.

Applications: Avidity testing is used in infectious disease serology to estimate the timing of infection and to support incidence surveillance. It is particularly associated with HIV testing to help classify infections as recent or established, which can inform epidemiological assessments. The test can also aid in evaluating congenital infections and other conditions where distinguishing recent from long-standing infection is clinically or epidemiologically useful. It is typically used as a supplementary test alongside other diagnostic markers.

Interpretation and limitations: A low avidity index generally indicates a recent infection, while a high index suggests a longer-standing infection; however, cutoffs vary by assay and pathogen. Results can be influenced by factors such as immunosuppression, antiretroviral therapy, very early infection before avidity maturation, vaccination, or maternal antibodies in neonates. Therefore, avidity results should be interpreted together with clinical information and other laboratory findings.

See also: avidity, immunology, ELISA, HIV incidence testing.