MONDAY, Sept. 29, 2008 (HealthDay News) -- The amount of bleeding in the brain that occurs when a blood vessel bursts and causes a stroke is greater for some people who take the clot-preventing drug warfarin (Coumadin), a new study shows.
It's not a surprising finding, said Dr. Daniel Woo, an associate professor of neurology at the University of Cincinnati and co-author of the report in the Sept. 30 issue of Neurology, since it's long been established that the risk of death from such a stroke is greater for people taking warfarin.
But there has been a debate about whether the increased risk is due to an increased volume of blood spewed into the brain. The study of 258 people who had brain hemorrhages appears to settle the issue, Woo said: "We did find a larger volume of hemorrhage in these patients."
This general finding might not impress the estimated millions of Americans, most of them elderly, who are taking warfarin for a variety of reasons, such as prevention of potentially stroke-causing clots due to the abnormal heartbeat called atrial fibrillation. It is also taken by people with artificial heart valves or who have tiny blood clots in the lungs.
However, another, more specific finding from the study could be very important to these people. The excess bleeding was seen only in warfarin users with an INR of 3 or greater. INR, the international normalized ratio, is a measure of the ability of blood to clot properly.
"Normally, the INR is less than 2," Woo explained. "On warfarin treatment, the goal is to keep it between 2 and 3. In our study, if it was greater than 3, it was associated with a higher initial volume of hemorrhage. Between 1.2 and 3, there was not a significantly higher volume of hemorrhage."
But one person's INR can vary unpredictably, so regular blood tests are needed to be sure it is within the desired range, Woo said. "INR levels go up and down quite a bit," he said. "If it is too high, you run the risk of hemorrhage. If it is too low, you run the risk of whatever it is you are trying to prevent in the first place."
One reason for taking warfarin is to reduce the risk of stroke caused by blockage of a brain artery by a clot. And so, the warfarin user must walk a fine line, reducing the ability of the blood to clot enough to prevent such a stroke but not too much, which can lead to the kind of stroke experienced by people in the study.
"It is very important to have regular testing for your INR level," Woo said.
"There are a variety of reasons to keep INR within that range," said study author Dr. Matthew H. Flaherty, an assistant professor of neurology at the University of Cincinnati. "If it is higher, the chances of bleeding go up. If it is lower, there is less bleeding to start with, and if there is bleeding, there will be less of it."
More information
Learn why warfarin is prescribed and precautions for its use from the U.S. National Library of Medicine.
