Medicine:Rapid antigen test

Rapid antigen test
Medical diagnostics
Synonyms	Rapid antigen detection test (RADT)
Purpose	To diagnose infections

A rapid antigen test (RAT) is a rapid diagnostic test suitable for point-of-care testing that directly detects the presence or absence of an antigen. This distinguishes it from other medical tests that detect antibodies (antibody tests) or nucleic acid (nucleic acid tests), of either laboratory or point of care types.

Common examples of RATs or RADTs include:

• Rapid strep tests (for streptococcal antigens)
• Rapid influenza diagnostic tests (RIDTs) (for influenza virus antigens)
• Malaria antigen detection tests (for Plasmodium antigens)

Antigen tests and antibody tests are often immunoassays (IAs) of one kind or another, such as dipstick IAs or fluorescence immunoassays. While RAT is an immunochromatographic assay which gives visual results that can be seen with the naked eye. It is considered to be qualitative but a person experienced in RDT testing can easily quantify the results. Being a screening test, the results should be evaluated on the basis of confirmatory tests like PCR testing or western blot.

One inherent advantage of an antigen test over an antibody test (such as antibody-detecting rapid HIV tests) is that it can take time for the immune system to develop antibodies after infection begins, but the foreign antigen is present right away. Although any diagnostic test may have false negatives, this latency period can open an especially wide avenue for false negatives in antibody tests, although the particulars depend on which disease and which test are involved.