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 which metal(s) is problematic in hopes of selecting an ideal device for the patient. So it is best to test with the individual metals. To the best of my knowledge, all available PFO closure devices in the US contain nickel.

Here is a helpful reference: Bahrani et al., PMID 31045931.