Which term is used to determine susceptibility to diphtheria?

The Schick test is the correct term used to determine susceptibility to diphtheria. This test is a diagnostic tool that assesses an individual's immunological response to the toxin produced by the diphtheria bacteria, Corynebacterium diphtheriae. In the Schick test, a small amount of diphtheria toxin is injected intradermally into the skin. If the individual is susceptible to diphtheria (meaning they have not been previously immunized or infected), a local skin reaction occurs, indicating a positive result. Conversely, individuals who have been previously immunized or infected will typically not exhibit a reaction, showing they have developed immunity to the diphtheria toxin.

The other tests mentioned serve different purposes. The Tokyo test is not specifically related to diphtheria susceptibility, and the purified protein derivative test is primarily used for tuberculosis screening. The skin prick test is commonly associated with allergy testing. Therefore, the Schick test specifically assesses susceptibility to diphtheria, making it the correct choice.