UrinantigenTest

Urinantigentest, or urine antigen tests, are diagnostic assays designed to detect specific microbial antigens in urine. They are used to rapidly identify certain bacterial pathogens that cause pneumonia and other infections, often as point-of-care tests or in clinical laboratories. The most common targets are Streptococcus pneumoniae (pneumococcal urine antigen test) and Legionella pneumophila serogroup 1 (Legionella urine antigen test). Many assays use immunochromatographic lateral flow technology or enzyme immunoassays to detect noncellular components such as capsule polysaccharides or lipopolysaccharides that are shed into urine during infection.

Procedure and interpretation: the test typically uses a clean-catch midstream urine sample. Results are usually available within minutes to a few hours. A positive result supports the presence of the corresponding infection, such as pneumococcal pneumonia or Legionnaires’ disease, and can be especially helpful when antibiotic therapy has already begun and culture yield is low. A negative result does not exclude infection, as sensitivity varies by pathogen, patient age, and disease severity.

Performance and limitations: specificity is generally high for Legionella UAT, often above 90%, while sensitivity varies and is commonly around 50–70% for pneumococcal UAT, with lower accuracy in some populations. Limitations include that tests may not detect all circulating strains or serogroups, cannot distinguish colonization from active infection, may persist as false positives after prior infection, and are not substitutes for comprehensive diagnostic workups that include culture or molecular methods.

Clinical use: urinantigentests are used as adjuncts in the workup of suspected pneumococcal disease or Legionnaires’ disease, guiding initial antibiotic choices and informing infection-control decisions when integrated with clinical assessment and other laboratory data.