How long before surgery should you stop blood thinners

What is the problem and what is known about it so far?

Doctors commonly give blood thinners (anticoagulants) to patients who are at risk for the formation of blood clots that can result from many medical conditions. Warfarin, a pill that is taken by mouth, is commonly used for its anticoagulant effect. Warfarin is both effective and convenient to take, but it requires a few days to achieve adequate anticoagulation after the first dose and its effect on blood clotting lasts for 3 to 5 days after patients have stopped taking it. When a patient taking warfarin must undergo surgery, doctors have to stop warfarin treatment about 5 days before the procedure because anticoagulation can cause excessive bleeding, especially when tissues are cut. On the other hand, when the patient is not protected by anticoagulation, the risk for a dangerous blood clot increases. Doctors often handle this dilemma by stopping warfarin treatment several days before surgery and substituting a drug from a class of anticoagulants known as low-molecular-weight heparin. One member of this class is enoxaparin, a medication that must be given by injection, either once or twice daily. Enoxaparin treatment also must be stopped shortly before surgery, but because its effect does not last as long as that of warfarin, it can be stopped a shorter time before surgery. Common practice is to give the last dose of twice-daily enoxaparin the evening before surgery. Once surgery is finished, enoxaparin treatment is restarted until warfarin therapy is resumed adequately. Using enoxaparin this way is known as “bridging” therapy.

Why did the researchers do this particular study?

To find out whether the anticoagulant effect of enoxaparin goes away when the last dose is given the evening before surgery (more than 12 hours before surgery) and whether performing surgery is safe at that time.

Who was studied?

94 consecutive patients who received bridging enoxaparin therapy.

How was the study done?

The researchers stopped giving warfarin 4 or 5 days before surgery and replaced it with twice-daily injections of enoxaparin 3 days before the surgical procedure. The last injection of enoxaparin was given in the evening and at least 12 hours before surgery. Blood tests were done on all patients just before they went to surgery to see how much anticoagulant was still in the bloodstream.

What did the researchers find?

Blood samples were drawn an average of 14 hours after the last dose of enoxaparin was given and surgery was performed an average of 97 minutes after blood samples were drawn. At least some anticoagulant activity was found in the blood of 99% of the patients. Of these patients, 68% had enough residual enoxaparin effect to be considered fully anticoagulated and 16% had even higher levels.

What were the limitations of the study?

Only 1 type of low-molecular-weight heparin was tested. Other types might have produced different results.

What are the implications of the study?

The last dose of enoxaparin before surgery should be given more than 12 hours and possibly as much as 24 hours before surgery.

Recent Blog Articles

Harvard Health Blog

August 10, 2020

• By Julie Corliss, Executive Editor, Harvard Heart Letter

Millions of people with cardiovascular disease take drugs that help prevent blood clots, which can lodge in a vessel and choke off the blood supply to part of a leg, lung, or the brain. These potentially lifesaving medications include warfarin (Coumadin) and a class of drugs called non-vitamin K antagonist oral anticoagulants or NOACs. Examples include dabigatran (Pradaxa) and rivaroxaban (Xarelto).

However, if you’re taking one of these drugs and need an invasive procedure — anything from a tooth extraction to a hip replacement — managing the risks can be tricky, says cardiologist Dr. Gregory Piazza, assistant professor of medicine at Harvard Medical School. "There’s a higher-than-normal risk of bleeding during and after the procedure, because your blood doesn’t clot as easily," he says.

But stopping an anticlotting drug is also risky. Doing so increases the chance of a blood clot, especially if you have surgery, which also leaves you more prone to a clot. "Walking the tightrope between these two extremes can be a challenge for clinicians," says Dr. Piazza. They need to consider if, when, and how long a person might need to stop taking their anticlotting medication. And the answer hinges on many different factors.

Different risk levels

Each year, about one in 10 people taking a NOAC requires a planned invasive procedure. These include diagnostic tests and treatments that require a doctor to use an instrument to enter the body. Some are more risky than others, of course. Minor procedures such as a skin biopsy aren’t very worrisome, because you can compress and bandage the wound, says Dr. Piazza.

Tooth extractions can bleed a fair amount. Compresses and topical treatments are usually sufficient for controlling the bleeding, although your doctor might suggest skipping your anticoagulant the day of the procedure.

Biopsies, injections, and surgeries

Deciding to stop an anticoagulant for a colonoscopy is more complicated. A diagnostic colonoscopy isn’t likely to cause bleeding. But if the doctor has to remove any polyps from the colon, the risk of bleeding rises. Other procedures that require careful planning for people on anticoagulants include breast and prostate biopsies, as well biopsies of internal organs, such as the kidney or liver, which can lead to hard-to-detect internal bleeding.

Another common procedure (especially in older people) is a steroid injection in the spinal column to treat back pain. This, too, may cause undetected and potentially dangerous bleeding around the spinal column in people taking anticoagulants.

People nearly always have to stop taking anticlotting medications a few days prior to any type of elective surgery. Sometimes, doctors will use injectable, short-acting anticlotting drugs right before and immediately after the operation. This technique, called bridging, helps them better balance the degree of blood clotting during that critical window of time.

A key conversation

In addition to the procedure itself, other factors that affect anticoagulant decisions include a person’s age, any other health problems or medications they take, and whether they’re taking warfarin (which stays in the body for days) or a NOAC (which may lose some of its effect after about 12 hours). Because of all these variables, the best strategy is to make sure that the doctor slated to perform your procedure talks directly with the doctor who prescribed your anticoagulant, says Dr. Piazza. "If that conversation doesn’t take place, patients can have problems with either bleeding or clotting," he says. Many physicians who do procedures aren’t as familiar with NOAC prescribing guidelines, so they may mistakenly keep people off these medications for a week or more, putting them at risk for a clot.

About the Author

Julie Corliss, Executive Editor, Harvard Heart Letter

Julie Corliss is the executive editor of the Harvard Heart Letter. Before working at Harvard, she was a medical writer and editor at HealthNews, a consumer newsletter affiliated with The New England Journal of Medicine. She … See Full Bio

View all posts by Julie Corliss

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No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

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