Schick test: Introduction, principle, procedure and result interpretation

Schick Test: Introduction, Principle, Procedure and Result Interpretation

Schick test for Corynebacterium diphtheriae causing diphtheria

Introduction of Schick test

Schick test is invented between 1910-1911, a test used to determine whether or not a person is susceptible to diphtheria, and the causative agent is Corynebacterium diphtheriae. It was named after its inventor Bela Shichk (1877-1967), a Hungarian-born American pediatrician. It is an intradermal test. The test is carried out by injecting intradermally into the skin of the forearm 0.1 ml of diluted (1/50 MLD) diphtheria toxin, while into the opposite arm is injected as a control, the same amount of toxin which has been inactivated by heat.

Principle of the test

The Schick test works by injecting intradermally into the skin of the forearm 0.1 ml of diluted (1/50 MLD) diphtheria toxin. If the person is susceptible to the disease, a red swollen rash appears around the injection area.

Procedure of Schick test

Inject toxin intradermally.
Wait for 2 to 4 days.

Observation of result

Check redness/erythematic production and measure the zone of reaction in mm.

Interpretation of Schick test result

Negative reaction: If a person had immunity to diphtheria, no reaction will be observed on either arm.

Positive reaction: An area of induration 10-15 mm in diameter generally appears within 24-36 hours reaching its maximum development by 4-7 days, the control arm shows no change. The person is susceptible to diphtheria.

False-positive reaction: A red flush develops in both arms, the reaction fades very quickly, and disappears by the 4th day. This is an allergic-type of reaction found in certain individuals
Combined reaction: the control arm shows pseudo positive reaction and the test arm is true +ve reaction, susceptible, and need vaccination

Keynotes

Schick test is not indicated in very young children as they are susceptible and require immunization
No reaction – Protective immunity present.
This test is now outdated due to vaccination and eradication.
It is also called the toxigenic test.
MLD stands for minimal lethal doses.

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