The NHS has issued a national alert over shortages of certain blood types.

National stocks of O negative and O positive blood have fallen to “unprecedentedly low levels” with increased demand from hospitals and high levels of unfilled donor appointments creating “a perfect storm”, NHS Blood and Transplant (NHSBT) said.

The alert means blood stocks have fallen to under two days’ worth, with 1.6 days of O negative – the universal blood group – left, while national stocks of all blood types is 4.3 days.

The NHS has issued an urgent appeal for more blood donors to come forward.

O group donors are being asked to urgently book and attend appointments at permanent donor centres or with one of the service’s 235 mobile blood collecting teams.

There are 45,000 appointments available between now and September.

NHSBT chief executive Dr Jo Farrar has described the situation as “critical”.

“We’re making an additional 1,000 appointments per week available, please take a moment to go online and book,” she said.

“If you can’t find an appointment immediately, please book in for coming days, weeks and months. We will have an ongoing need for donations.”

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O negative is used in emergencies or when a patient’s blood type is unknown. It is typically carried by air ambulances and emergency vehicles – and makes up around 16% of hospital blood orders.

NHSBT has written to hospitals asking them to restrict the use of O blood types to essential cases and where possible, use substitutions.

The alert means hospitals can implement emergency measures to minimise usage and move staff to work in laboratories to monitor the use of O type blood.

It is just the second time such an alert has been issued, with the only other occasion coming in October 2022.

The ongoing cyber incident which affected several London hospitals in June has impacted blood stocks, with a 94% increase in demand for O negative compared to the same time last year.

A number of hospitals declared critical incidents, cancelled operations and were left unable to carry out blood transfusions after the ransomware attack on pathology firm Synnovis.

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Blood has a shelf life of 35 days and there are just under 800,000 regular donors in the UK, NHSBT’s chief medical officer said.

Dr Gail Miflin continued: “Ultimately, we need more people to be regular blood donors and come to one of our 25 donor centres.”

Women can donate blood once every four months and men can do so once every three.

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