If they had discovered something really awful they would have made a much bigger fuss.
I'm presuming you had some blood tests because they were looking for something, right? So the fact they want to discuss the results means that perhaps they found something (I can't speculate more than that as I don't know what symptoms you had and what they were testing for) that answers your questions. This could be a good thing as it means you have an answer, or it could mean that more needs to be done. Either way, don't stress yourself out too much, and just call them back when you can.