Britain should prepare for shortages of blood because the number of donors is dropping and concerns about the human form of mad cow disease could dent supplies, an expert said on Friday.

“We need to act now to decrease our dependence or we will be faced with deciding which patient is going to get the remaining bag of blood…with all the clinical and ethical problems that will ensue,” said Adrian Copplestone, of Derriford Hospital in Plymouth.

In an editorial in the British Medical Journal, he said the government had already tightened regulations for blood donors following the announcement of a second possible case of Creutzfeldt-Jakob disease (vCJD) transmitted through a blood transfusion.

The move, coupled with a general trend of fewer donors, means hospitals must use blood more effectively.

The Department of Health recently circulated a plan to deal with blood shortages. It suggests that elective surgery that has more than a 20-percent chance of requiring blood should be the first to be cancelled.

There is also a move to reduce blood transfusion errors.

“We all need to use blood appropriately,” Copplestone added.