But a new study turns that well-accepted tenet on its head, with evidence that, for some patients, doing so could dramatically increase their risk of stroke.
"What this study does is raise some serious questions about the application of current guidelines that recommend stopping anti-clot medications prior to invasive procedures," says study author Dr. Stanley Cohen. "And hopefully [it] will shed some light on other ways to manage treatment for these patients if and when they require some type of surgical procedure."
Cohen, director of the Stroke Program at Cedars-Sinai Medical Center in Los Angeles, presented his findings Thursday at the annual meeting of the American Academy of Neurology in Honolulu.
The study focused on a sub-group of stroke patients with a cardiac condition known as "atrial fibrillation." This is a type of heart-rhythm disturbance that affects more than 2 million people, and it dramatically increases the risk of blood clot formation, and, ultimately, stroke.
While all types of strokes can be devastating, the type that occurs because of atrial fibrillation "can yield the greatest amount of damage and disability," Cohen says.
One way that warfarin reduces that risk is by thinning the blood, keeping clots from forming. But that also increases the risk of hemorrhage, should any type of bleeding occur. This is one reason why doctors routinely tell patients to stop taking this drug up to seven days before surgery, says Cohen.
However, many types of surgeries -- including dental work, skin biopsies, mole removals, and even colonoscopies (without polyp removal) -- carry a slight risk of major bleeding, he says.
"When this is the case, the risk of stroke is far greater than the risk of hemorrhage," says Cohen, who adds that stopping the drug could have dire consequences.
Proving that, he says, was the point of the new study.
The researchers examined the medical records of more than 650 patients admitted to Cedars-Sinai Medical Center for treatment of stroke. From this group, they identified 178 patients who had been previously diagnosed with atrial fibrillation and were taking warfarin for stroke prevention.
The researchers then identified 14 patients who had discontinued warfarin up to seven days before some type of elective surgery.
"All 14 -- 7 percent of the total group -- had strokes within the seven days prior to surgery when they were not on warfarin, or within one to three days afterwards, " says Cohen. Nine of the 14 were seriously disabled as a result of those strokes.
The study conclusion: "Our findings indicate that a good deal of the atrial fibrillation-related strokes can be prevented if patients do not discontinue the use of anti-clotting medications for a prolonged period of time prior to surgery," says Cohen.
It's a conclusion that neurologist Dr. Keith Siller says is important and accurate.
"This gives us some evidence of what many stroke experts have known for a long time -- there is a better way to treat these patients, and the conventional wisdom of discontinuing ant-clot medication before surgery is not always the right thing to do," says Siller, medical director of the New York University Comprehensive Stroke Care Center.
One of these "better ways" is to weigh the odds of bleeding from the procedure, against the odds of having a stroke, before deciding if and when to stop warfarin therapy, Cohen and Siller say.
But there's another alternative, according to Cohen. Two different forms of the drug heparin -- another blood-thinning treatment -- are available and can be used in place of warfarin prior to surgery.
With both treatments, there's a decreased risk of bleeding similar to that which occurs with warfarin, without increasing the risk of stroke.
However, both forms of heparin are expensive -- one requires intravenous administration in a hospital setting for a week prior to surgery. As a result, insurance-company spending limits often keep patients from learning all their options.
"I think any patient with atrial fibrillation who is taking warfarin has the right to know that stopping their medication could put their life at risk, and that they don't have to take that risk because there are other treatments that can help," says Cohen.
Siller agrees: "Patients should be told -- they need to know all their options. And hopefully, this study will help spread the word that there is a better way."