A physician attempting to diagnose a metal allergy will conduct a full physical examination of the patient. Compiling a medical history and a list of symptoms is also necessary.

Most physicians use a skin patch test to diagnose metal allergies. During this test, an absorbent pad will be soaked with suspected metal allergens and taped onto the skin of the patient for 24 to 72 hours. The amount of metal allergen on the pad should not cause any reaction in people not allergic to the metal. However, those who are allergic to the metal should react with a rash or wheal.

It can be very difficult in skin testing to distinguish between a nickel allergy and a cobalt allergy. Nickel and cobalt are found together in alloys and salts because it is too costly to separate the two metals. This is a problem in testing situations, as it is very difficult to obtain pure solutions of the individual metals. Therefore, patient history will be crucial to helping determine whether a patient is allergic to nickel, cobalt or both.