Schick test

The Schick test, invented between 1910 and 1911 is a test used to determine whether or not a person is susceptible to diphtheria. It was named after its inventor, Béla Schick (1877–1967), a Hungarian-born American pediatrician.

The test is a simple procedure. A small amount (0.1 ml) of diluted (1/50 MLD) diphtheria toxin is injected intradermally into the arm of the person. If a person does not have enough antibodies to fight it off, the skin around the injection will become red and swollen, indicating a positive result. This swelling disappears after a few days. If the person has an immunity, then little or no swelling and redness will occur, indicating a negative result.

Results can be interpreted as:
 * 1) Positive: when the test results in a wheal of 5–10 mm diameter
 * 2) Pseudo-positive: when there is only a red colored inflammation and it disappears rapidly
 * 3) Negative reaction:
 * 4) pseudo negative reaction:

The test was created when immunizing agents were scarce and not very safe, however as newer and safer toxoids were made available there was no more requirement for susceptibility tests.