Thallium Side Effects

I had a thallium stress test 8 days ago and passed with flying colors; HOWEVER, within 3 days I developed hives which will not go away, despite taking a daily 10mg certirizine hydrochloride tablet and using a 1% hydrocortisone cream. MD's nurse did not return my last Fri. phone call and cannot reach office until tomorrow. How ;long will this last?

[Cleveland Clinic]

I am not sure.  The hives occurring 3 days later doesn't really sound like an allergic reaction to the thallium.  I have actually never seen anything like this before but will look into it.  Regardless, most of these go away within 7 days.  If they don't I would suggest seeing a dermatologist.  This could be something completely unrelated.