An appeal has been launched for O blood-type donors to book appointments across the country following the ransomware attack affecting major London hospitals.

NHS Blood and Transplant is appealing for O blood-type donors to book appointments to donate as this is safe to use for all patients and the IT attack means the affected hospitals cannot currently match patients’ blood at the same frequency as usual.

It comes after several London hospitals declared a critical incident, cancelled operations and tests, and were unable to carry out blood transfusions this week after the attack on the pathology firm Synnovis, which Qilin, a Russian group of cyber criminals, is understood to have been behind.

Memos to NHS staff at King’s College Hospital, Guy’s and St Thomas’ (including the Royal Brompton and the Evelina London Children’s Hospital) and primary care services in London said a critical incident had been declared.

Now NHS Blood and Transplant is calling for O-Positive and O-Negative blood donors to book appointments in one of the 25 NHS Blood Donor Centres in England to boost stocks.

The hospitals affected by the cyber attack cannot currently match patients’ blood at the same frequency as usual, NHS Blood and Transplant said.

For surgeries and procedures requiring blood to take place, hospitals need to use O type blood as this is safe to use for all patients and blood has a shelf life of 35 days, so stocks need to be continually replenished, the NHS added.

That means more units of these types of blood than usual will be required over the coming weeks.

O-negative is the type that can be given to anyone, known as the universal blood type.

It is used in emergencies or when a patient’s blood type is unknown.

Air ambulances and emergency response vehicles carry O negative supplies.

Just 8% of the population have type O Negative but it makes up for around 15% of hospital orders.

O positive is the most common blood type, 35% of donors have it, and it can be given to anybody with any positive blood type. This means three in every four people, or 76% of the population, can benefit from an O-positive donation.

This National Blood Week it has been revealed that three blood donations are needed every minute in hospitals and there are about 13,000 appointments available nationally this week in NHS Blood Donor Centres with 3,400 available in London.

Dr Gail Miflin, chief medical officer, NHS Blood and Transplant, said: “Patient safety is our absolute priority.

“When hospitals do not know a patient’s blood type or cannot match their blood, it is safe to use O-type blood.

“To support London hospitals to carry out more surgeries and to provide the best care we can for all patients, we need more O Negative and O Positive donors than usual.

“Please book an urgent appointment to give blood at one of our 25 town and city donor centres which currently have good appointment availability.

“We have availability for donors who know they are type O but we also welcome new donors who don’t yet know their blood type.

“You might have one of these special types that can be used in emergencies.”

Professor Stephen Powis, medical director for NHS England, said: “NHS staff are continuing to go above and beyond to minimise the significant disruption to patients following the ransomware cyber-attack on Synnovis earlier this week.

“Urgent and emergency services are available as usual so patients should access services in the normal way by dialling 999 in an emergency and otherwise use NHS 111 through the NHS App, online or on the phone.

“But unfortunately, we know that a number of operations and appointments have been postponed or diverted to other neighbouring hospitals not impacted by the cyber-attack, as we prioritise pathology services for the most clinically urgent cases.

“To help London staff support and treat more patients, they need access to O-Negative and O-Positive blood, so if one of these is your blood type, please come forward to one of the 13,000 appointments currently available in NHS Blood Donor Centres.”

Following the bank holidays and school half-term holidays, the NHS currently has lower than normal stocks of type O blood and is urging known O-group donors to come forward and make an appointment in town and city donor centres across the country including London, Bristol, Birmingham, Cambridge, Nottingham, Manchester and Newcastle, NHS Blood and Transplant said.

For more information search GiveBlood online and on social media or visit Blood.co.uk