BIOLAB in London does biocompatibility tests through a blood sample, for a reasonable price of about £50 (at least when I had one done). I think it is a good idea to have the test done, especially if you have multiple sensitivities. Unfortunately I didn't get a chance to have a test done for my last round of filling replacements as my dentist had changed material (no longer uses diamondlite but glacier) so am just hoping for the best.