Poorest procedure to determine allergy (4,4)

I believe the answer is:

skin test

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'allergy' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

I can't explain the remainder of the clue.

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(Other definitions for skin test that I've seen before include "medical procedure?" , "Medical check" , "Check for allergy" , "Trial to determine immune reaction" .)

I've seen this clue in The Sunday Times and The Times.

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