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. 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.