The NHS is making an urgent appeal for blood donors - particularly people who are O negative - as stocks run low.
Further bouts of bad weather in the coming days are expected to lead to more shortages of blood, according to NHS Blood and Transplant.
Stocks of O negative blood have fallen below "preferred levels", with just 1,928 units left in store (each unit is just under a pint).
Only 7% of the population are O negative - a key type that can be given to anybody.
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 NHS also wants people who donate blood platelets to come forward as they only have a shelf life of five days, meaning stocks need to be replenished regularly.
A total of 69 donor sessions were cancelled in one week during the worst of the recent weather in England and North Wales, figures show.
Even those centres that managed to hold sessions saw fewer donors coming through the doors.
Jon Latham, assistant director of blood donation at NHSBT, said: "We would like to thank everyone who has given blood over the past few weeks, particularly when the weather was bad.
"We rely on the generosity and commitment of volunteer donors to help us maintain the vital supply of blood to hospitals.
"To boost stocks we need to ensure that we make the most of the sessions that are going ahead to try to make up for the cancellations in other areas and urge donors to make every effort to attend if they possibly can.
"We especially need O negative donors at the moment as we have experienced higher than expected orders for this type of blood in the past week.
"With Christmas rapidly approaching and the holidays this year falling over a weekend, we would also like to remind anyone due to donate to step forward now, weather permitting.
"Maintaining healthy stocks of all blood groups is essential as people will still be in hospital and requiring treatment."