The Schick test, developed in 1913, is a
skin test
A skin test is a medical test in which a substance is injected into the skin.
Examples
* Casoni test
* Corneometry
* Dick test
* Fernandez reaction
* Frei test
* Hair perforation test
* Kveim test
* Leishmanin skin test
* Lepromin
* Patch t ...
used to determine whether or not a person is susceptible to
diphtheria
Diphtheria is an infection caused by the bacterium '' Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and s ...
.
It was named after its inventor,
Béla Schick
Béla Schick (16 July 1877 – 6 December 1967) was a Hungarian-born American pediatrician. He is the founder of the Schick test. Bela Schick was born in Balatonboglár, Hungary, and brought up in Graz, Austria, where he attended medical s ...
(1877–1967), a Hungarian-born American pediatrician.
Procedure
The test is a simple procedure. A small amount (0.1 ml) of diluted (1/50
MLD) diphtheria toxin is injected intradermally into one arm of the person and a heat inactivated toxin on the other as a control. If a person does not have enough
antibodies
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
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:
[Preventive and Social Medicine, Park 22nd edition, pg 151]
# Positive: when the test results in a wheal of 5–10 mm diameter, reaching its peak in 4–7 days. The control arm shows no reaction. This indicates that the subject lacks antibodies against the toxin and hence is susceptible to the disease.
# Pseudo-positive: when there is only a red-colored inflammation (
erythema
Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not assoc ...
) and it disappears within 4 days. This happens on both the arms since the subject is immune but hypersensitive to the toxin.
# Negative reaction: Indicates that the person is immune.
# Combined reaction: Initial picture is like that of the pseudo-reaction but the erythema fades off after 4 days only in the control arm. It progresses on the test arm to a typical positive. The subject is interpreted to be both susceptible and hypersensitive.
The test was created when immunizing agents were scarce and not very safe; however, as newer and safer
toxoids
A toxoid is an inactivated toxin (usually an exotoxin) whose toxicity has been suppressed either by chemical (formalin) or heat treatment, while other properties, typically immunogenicity, are maintained. Toxins are secreted by bacteria, whereas ...
became available, susceptibility tests were no longer required.
References
* ''Taber's Cyclopedic Medical Dictionary'', 20th Ed. (2005).
{{Immunologic techniques and tests
Skin tests
Pediatrics
Diphtheria
Immunologic tests