THE NHS has put out an urgent 'amber alert' after "a perfect storm" from recent cyber attacks and low donation numbers has seen national blood stocks "drop to unprecedentedly low levels". NHS Blood and Transplant (NHSBT) issued a callout for to replenish stocks O-negative and O-positive blood, which are running dangerously low. It said current national stocks of O-negative blood will last 1.

6 days, while overall national stocks of blood across all types will last 4.3 days. O blood-type is important because it is 'universal' - regardless of a person's blood type, they can receive a transfusion with O blood in most cases.

Blood has a shelf life of 35 days, so stocks need to be continually replenished. Hospitals need use O-type blood for surgeries and procedures requiring blood, as well as when a person's blood type is not known, according to the NHS. But - to put things in perspective - just 8 per cent of the population have type O-negative, but it makes up for around 16 per cent of hospital orders.

"O-negative and O-positive donors are asked to urgently book and fill appointments at donor centres," it said in an alert issued today. NHSBT also wrote to hospitals asking them to restrict the use of O blood "to essential cases", using different types "where clinically safe to do so". "A perfect storm of increased demand of O type blood from hospitals following the recent cyber attack - which has impacted London hospitals - and reduced collections due to high levels of unfilled app.