Schick test /shik/ [Bela Schick, Austrian-American physician, 1877–1967] , a skin test formerly used to determine immunity to diphtheria in which dilute diphtheria toxin was injected intradermally. A positive reaction, indicating susceptibility, was marked by redness and swelling at the site of injection; a negative reaction, indicating immunity, was marked by absence of redness or swelling. This test, along with vaccination, was a major factor in the reduction of diphtheria from epidemic proportions in the 20th century to an extremely rare occurrence.
