For a contact allergy, do you need to test for the metals individually or does it suffice to just test with a piece of metal from the device?

I asked Dr. Brandon Adler about this question and he said:

Testing with metal discs or samples from a manufacturer is not recommended because irritant reactions, false negatives, and false positives are known to occur. Even if there were to be a true positive reaction, there would be no way to know w...