My understanding, from very preliminary research on this, is that he can still have heparin in certain instances, like surgery for example, because there aren't all that many alternatives to heparin available, but they have to be very cautious and be on the lookout for thromboses or clots which can be very dangerous. One article suggested aspirin therapy prior, most likely so they can use less heparin.
http://ukidney.com/This site is free to register on and you can directly ask a doctor there if you like. I'll keep trying to find stuff on this but for now I'm off to D.