English hospitals face being "named and shamed" for not screening patients for deep vein thrombosis (DVT) risk, NHS medical director Sir Bruce Keogh has said.
NHS trusts are required to screen 90% of hospital patients.
But fewer than half manage this says the NHS, which warns 25,000 people die each year from hospital-acquired DVT.
One assessed just one in four patients and another barely one in 10. Sir Bruce said this was "absolutely disgraceful".
"In the sort of NHS that I want to work in and be treated in, I don't think that level of practice is acceptable."
DVT involves blood clotting in the legs and can be fatal if a clot breaks off and travels in the blood up to the lungs and causes a blockage, known as a pulmonary embolism.
Since April 2010, trusts in England have faced losing up to 0.3% of their income for failing to meet the guidelines. Some have already lost money. And there will continue to be financial consequences for trusts who do not meet the target, Sir Bruce Keogh told BBC Radio 4's Face the Facts.
He also says he will name the worst performers if they continue to do badly.
Giselle Dye's mother Giska was admitted to Worthing Hospital in Sussex in January following a fall and with suspected internal bleeding. She was not assessed for DVT, which killed her.
"To my mind it's such a simple procedure they should be able to get this right," said Giselle. "If they had done the risk assessment they might have been able to make sure my mother's legs were elevated."
"My mother was left sitting in a chair. The carer took a photograph the day before she died and her legs from the knee down were dark purple. Your legs don't go dark purple unless you have been sitting for a very long time without moving."
Western Sussex Hospitals Trust, which runs Worthing Hospital, has apologised for not assessing Mrs Dye and for other shortcomings in the care provided.
But director of nursing and patient safety Cathy Stone said: "I am unable to talk directly about Mrs Dye's case but it is important to remember that treatment for VTE (vein thromboembolism) is not always appropriate."
The trust is now assessing 93% of patients and is aiming higher.
Risk factors for DVT include being immobile or bed-ridden for a long time and undergoing extensive surgery.
Preventative measures include blood-thinning drugs and compression stockings. But medication may not be appropriate in cases of internal bleeding or poor circulation.
Keeping patients mobile and hydrated is also important.
"Preventative treatment does reduce almost to zero the incidence of DVT," said John Black, the outgoing president of the Royal College of Surgeons.
"This is the number one clinical priority for me and my colleagues," said Sir Bruce.
"Some 25,000 people die a year from something that is preventable. The same sort of number which die from stroke and other major conditions which are far less preventable.
"Of course this is fairly early on in this initiative but we need to be firm about those that are failing to improve."
Radio 4's Face the Facts investigates DVT screening at 1230 BST on Wednesday 13 July, repeated at 2100 BST on Sunday 17 July, in the first of a new series of investigations.