Schick test procedure, interpretation (Dephtheria test)

Schick test procedure is used to demonstrate the level of antibodies in the blood of a person, who is either immunized or was previously infected by the dephtheria.

Schick test procedure

  • One Schick test dose of the toxin is injected intradermally in one forearm and the same amount of heated toxin is injected into the other forearm as a control.
  • The test is read three times, at 24 hours, 72 hours and then at 6 days. In a positive reaction, there is redness and swelling which increases for several days and then fades away.
  • The control arm does not show any reaction.
  • In the case positive schick test, there is not enough anti-toxin in the blood and such individuals are susceptible to diphtheria.
  • In a negative reaction, there is no reaction on either of the arms. Such an individual has an adequate level of anti-toxin in the serum and so is immune to diphtheria.
  • In the case of Pseudo reaction due to hypersensitivity to materials rather than the toxin in the injection, there is redness and swelling in both arms that disappears on both arms within 2-3 days. It is considered as negative Schick test.
  • In a combined reaction, a combination of a pseudo-reaction and a positive reaction occurs. In this, redness and swelling appear in both of the arms but in the control arm redness disappears in 2-3 days while in the other arm the reaction continues as in a positive reaction.
    1. In this the individual is hypersensitive to the material of the injection as well as susceptible to the diphtheria toxin.

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