
The NHS Blood and Transplant Service said stocks of O negative have fallen below "preferred levels."
O negative is an a key blood type because it can be given safely to patients in other blood groups.
The service, which covers England and north Wales, warns the return of the wintry weather could make the situation even worse.
O negative is the only safe option when a patient's blood group is unknown or not immediately available.
This means it is vital in emergencies and for procedures on unborn babies.
The Welsh Blood Service is also appealing for donors. It particularly wants O negative and A positive donors to come forward.
The service had to close its sessions early today, due to adverse weather.
In Scotland, the Scottish National Blood Transfusion Service said that stocks were holding up well, thanks to the response from donors there to appeals last week.
However Dr Moira Carter of the service said they were still aiming to build stocks up in the run up to Christmas.
Cancelled sessions
Sixty-nine blood donation sessions were cancelled in one week across England and North Wales during the worst of the weather.
At the sessions which did take place, fewer donors attended than would normally have been expected. ...................
Read the article in full at http://www.bbc.co.uk/news/health-12020215