The study found that the risk of developing a blood clot after surgery is higher than previously thought, and remains high for up to three months.
Prof Sheila Bird, MRC Biostatistics Unit, Cambridge, said:
“That there is a serious risk of blood clot after surgery is well known. Indeed, hospitals take measures to address it – by anticoagulation and the wearing of surgical stockings. But what is interesting about this study is that it examines the pattern of risk over the first 12 weeks following an operation, and subsequently.
“Over a 12 week period without surgery about 1 in 6,200 middle aged women is hospitalised (or dies) from venous thromboembolism. This 12-week absolute risk increases to 1 in 140 women after an inpatient operation; and is 1 in 815 women during the 12 weeks after a day case operation.
“The relative risk of venous thromboemolism peaks at three to four weeks after inpatient surgery – when most patients will already have been discharged. Hospitals need to re-emphasise the precautions that patients need to take following surgery, and in particular once they have left the hospital as this is clearly when much of the problem occurs.
“We should also remember when interpreting this study that individuals who undergo surgery are not a random sample. Indeed, this is underscored by the authors’ finding that, more than a year post-operation, their risk of thromboembolism is twice as high as for those women who needed no surgery.”
Dr Tim Chico, Senior Clinical Lecturer and honorary Consultant Cardiologist, MRC Centre for Developmental and Biomedical Genetics & NIHR Cardiovascular Biomedical Research Unit, University of Sheffield, said:
“This is an important study and we should be very grateful to the million women volunteers who made it possible. It is crucial to recognise risk of DVT after surgery, and we need to improve its prevention. I hope this research helps patients understand the need for things like compression stockings and blood thinning injections. DVT doesn’t only strike people undergoing surgery, so it is also important to avoid obesity and other risk factors.”
Dr Trevor Baglin, Consultant Haematologist at Addenbrookes Hospital, Chairman of the British Committee for Standards in Haematology, and Former member of the Department of Health Implementation Working Group for the prevention of Venous Thromboembolism in hospitalised patients, said:
“This is an extremely timely and informative publication. It comes following the Chief Medical Officer’s stated desire that all patients admitted to hospital should be assessed for risk of hospital-acquired thrombosis. The study defines the absolute and relative risk of venous thrombosis following surgery and indicates that there is a 70-fold increased risk attributable to surgery in the 6 weeks following an operation and that risk continues thereafter. Obviously, similar information on non-surgical patients would be extremely helpful.
“At the moment risk assessment for hospital acquired thrombosis is not mandated and interestingly many of the highest ranking hospitals in the recently reported Dr Foster Quality Accounts were unable to submit data on compliance with risk assessment, whilst others reported implementation between 0% and 50%. Clearly, the quality of this information is questionable but the figures are entirely compatible with what we already know is happening in hospitals around the country. There is a long way to go in the prevention of hospital acquired thrombosis and until it is given the same priority as hospital acquired infection and dealt with accordingly I think it is going to be a long and tortuous route to universal implementation of risk assessment and appropriate prophylaxis.”