Schick test, diagnostic test designed to evaluate susceptibility to diphtheria. A small amount of diphtheria toxin is injected into the skin; the injection will produce an area of redness and swelling in individuals with low levels of antibody (i.e., little immunity) against the toxin. If the individual is immune to diphtheria, the antibody in the system will neutralize the toxin and no skin reaction will occur.
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