A report by the American Medical Association has claimed that healthcare applications using RFID can induce electromagetic interference in medical equipment. In 123 tests, RFID induced 34 EMI incidents, 22 of them "hazardous". The report concludes that international standards may need to be updated in the light of the risk.
The work was carried out at the University of Amsterdam and the abstract is reported here. The report has also been followed up by RFID Journal here.
Clearly, given that RFID is already finding its way as an application into hospitals this study needs to be followed up. The idea that international standards need to be updated may be a concern, given the glacial pace at which standards usually move. I would guess there would need to be wider studies confirming the RFID electromagnetic interference issue on medical equipment before much will happen on the standards front.