Antikroppstitel

Antikroppstitel, or antibody titer, is a measure of the concentration of a specific antibody in a biological sample. It is defined as the greatest dilution of the sample that still yields a positive result in a particular serological test. The titer is usually reported as the reciprocal of that dilution, for example 1:80 or 1:160.

Measurement methods and interpretation can vary by assay. Common approaches include enzyme-linked immunosorbent assay (ELISA), in which an optical readout above a predefined cutoff indicates a positive reaction and the endpoint dilution determines the titer; or neutralization assays, where the dilution at which antibodies can prevent a functional effect is recorded. Titers may also be expressed as binding antibody titers or functional (neutralizing) antibody titers. In some contexts, specialized assays such as hemagglutination inhibition are used.

Interpretation of titers depends on the pathogen and the test. Generally, higher titers indicate a greater concentration of specific antibodies. However, a high titer does not always equate to protection, and protective thresholds vary by disease and assay. Titers can wane over time after infection or vaccination, and booster immunizations may raise them again. Laboratory variability and lack of universal standardization can affect comparison of titers across laboratories and assays.

Clinical uses include assessing prior exposure, evaluating vaccine responses, determining serostatus for blood donation or transplantation, and guiding follow-up for certain infections. Limitations include assay-dependent cutoffs, cross-reactivity, and the fact that seronegativity does not always exclude immunity.