Nearly 11,000 hospital patients may have died unnecessarily of blood clots due to a failure to implement treatment guidelines, say MPs.
All patients are supposed to be checked
The government announced in April that every hospital patient in England should be assessed to check their risk of deep vein thrombosis (DVT).
But the All-Party parliamentary Thrombosis Group found just 32% of trusts were taking the required action.
Up to 10% of all hospital deaths may be down blood clot complications.
DVT risk factors
Oral contraceptive pill
Clots most commonly form in the deep veins of the legs. They can be fatal if parts break off and lodge in small vessels of the lungs.
The MPs' report estimates that unnecesary DVT deaths in the last seven months may be three times as high as thoses from hospital acquired infections, such as MRSA and C. difficile.
This is despite the fact that the NHS plans to spend more than five times more fighting these so-called superbugs than on DVT prevention.
The parliamentary group is calling for the treatment guidelines - issued by the Chief Medical Officer for England - to be made mandatory.
Many at risk
John Smith MP, a group member, said: "DVT causes over 25,000 deaths each year.
"It is worrying that some NHS trusts are still failing to adhere to these guidelines, which could reduce deaths by over 40%
"How long will it take for NHS Trusts to start acting on this guidance and start saving lives?"
It is estimated that 52% of hospital patients are at risk of developing DVT.
However, the MPs' report said that less than half are made aware of the risks, and only a third will be risk assessed by a healthcare professional.
DVT has a mortality rate of 30% when left untreated - but this drops to just 2%-8% with appropriate therapy.
Dr Beverley Hunt, Medical Director of the thrombosis charity Lifeblood, said DVT was estimated to cost the NHS £640m a year.
She said: "It's deeply concerning that the simple step of risk assessing patients is not being taken.
"Any unwell adult entering a hospital bed has a 17% risk of DVT, but this risk rises considerably if you are over 40, are having surgery or have a pre-disposing condition such as cancer."
A Department of Health spokesperson said an implementation working group had been set up to drive forward the CMO's recommendations.
"We are also working hard to raise awareness of VTE amongst clinicians and patients."