When I went to fedex they denied me at first because as it turned out they have special packaging requirements when shipping blood and the package my vet gave me did not satisfy the requirements.
They almost allowed me to ship my package until some fedex rep on a power trip showed up and started telling me that they do not ship blood at all. After calling their customer service in front of him it turned out that in order to be shipped, it has to be in a double container, where if the blood vile inside breaks the blood will still be contained in an outer container.
Luckly the vets office was not too far and he new what that meant. The vet put the blood viles in a second sealed plastic container, and taped packages with dried ice around that. Fedex seems to be very strict about these requirements and I had to argue with them quite a bit that day.