My brother's blood levels were "off" a couple of times too, but his chemo wasn't postponed.

He did have an allergic reaction to something in the chemo treatment room (I can't remember which drug it was). The nurse gave his a shot of Benedryl and the reaction stopped immediately. After that, he receieved Benedryl via the IV (along with lots of fluids) first and then followed up with the chemo. It led to long chemo days, but he didn't have any more allergic reactions.