antigenpositive

Antigen-positive is a term used in laboratory testing to indicate that a specific antigen has been detected in a sample. An antigen is a molecule or part of a molecule that can provoke an immune response, frequently derived from a pathogen, but it can also be a host or tumor-associated protein. The designation "antigen-positive" implies that the test has found evidence of the target antigen and that the sample contains something the assay is designed to recognize.

Detection methods rely on antigen–antibody interactions. Common platforms include immunoassays such as ELISA, rapid lateral flow tests, and other antigen-detection technologies. A positive result suggests the presence of the antigen in the tested material, which can support a diagnosis, indicate current infection, or reveal the expression of a biomarker. However, interpretation depends on the clinical context and test characteristics.

In infectious disease testing, antigen positivity can signal active infection or recent exposure, but the timing of antigen appearance and test sensitivity can influence results. For example, p24 antigen testing and hepatitis B surface antigen (HBsAg) testing are used to identify HIV infection and hepatitis B infection, respectively. In oncology and research, detection of tumor-associated or surface antigens by methods like flow cytometry aids in diagnosis, prognosis, and treatment decisions.

Limitations include the possibility of false positives due to cross-reactivity and false negatives at low antigen levels or with improper sample handling. Positive antigen status is typically confirmed and interpreted alongside clinical findings and other laboratory results to reach a diagnostic conclusion.