**should read - metals, not metasl**
You are correct Razor. My thinking was more in line with nickel, stainless steel and metals of that type. The titanium and cobalt crome are used more frequently in surgical implants (not dentistry) because they hold less risk of an allergic response. Regardless, any allergenic symptoms would manifest within a short time after the surgery, not years later. Headaches, vomiting, inflammation would likely have keyed a physician to any problems during recovery.
The test will tell you if there is an issue with metasl, but the outlook of having more surgery to remove pins is something to be considered. As well as what may be used in their place that would be strong enough to hold your body on a weightbearing limb.
You could possibly be having an allergic reaction. You can confirm/rule out an allergic reation to implants with a Melisa test. Visit Melissa.org to learn more about implant allergies. The chances of having an allergic reation are quite small.
Titanium, cobalt and chrome are metals.
If your body were rejecting the metal you would have noticed inflammation and other problems long ago. The screws may not be metal at all, but titanium or cobalt crome. Were this going to present complications you would notice them shortly after surgery and your surgeon would have picked up on it also.
Good question. Take care.