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Infections May Trigger Dangerous Blood Clots

Respiratory, urinary tract problems linked to deep vein thrombosis, study suggests

THURSDAY, March 30, 2006 (HealthDay News) -- Infections can lead to heart attacks and strokes, and now British researchers say they have found they may also lead to deep vein thrombosis (DVT).

DVT is a blood clot that develops in a deep vein, usually in the lower leg. It can cause pain in the leg and potentially lead to complications, ranging from the relatively benign -- painless swelling of the leg -- to incapacitating -- chronic pain and leg sores. In worst cases, DVT can progress to a life-threatening pulmonary embolism, where a blood clot breaks free and enters the lungs.

In a report in the April 1 issue of The Lancet, Liam Smeeth, an epidemiologist with the London School of Hygiene and Tropical Medicine, and colleagues conclude that infections may trigger DVT.

"Infection has often been suggested as a possible risk factor for deep vein thromboembolism, but the evidence has been inconsistent and potentially biased," Smeeth said. "We think this study really establishes that infection is a risk factor for venous thromboembolism."

Both respiratory and urinary tract infections increase the risk for DVT, especially in the first two weeks after infection, Smeeth said. "The fact that the risk was raised by two different types of infection suggests that the risk of DVT may be due to the infectious process itself rather than a specific type of infection," he noted.

In their study, the researchers collected data on 7,278 patients who had DVT. They found that infections increased the risk of DVT by 20 percent, particularly during the first two weeks after infection.

Based on this finding, Smeeth thinks doctors should be aware of this connection. "In assessing a patient with a suspected deep vein thrombosis or pulmonary embolism, a history of recent or current infection should increase clinical suspicion and supports the diagnosis of venous thromboembolism," he said.

Doctors also need to recognize that patients with infections are at heightened risk of DVT, particularly those already at high risk, such as cancer patients or people taking long-distance flights, Smeeth said. "The presence of infection should inform decisions about the use of prophylactic measures to prevent venous thromboembolism," he added.

Dr. Suresh Vedantham, an assistant professor of radiology and surgery at Washington University Medical School in St. Louis, thinks this study confirms that infections, or more specifically, inflammation, can play a role in DVT.

It's "an interesting article which strengthens the already-suspected relationship between venous thromboembolism and infection/inflammation," he said.

Any infection triggers an inflammatory response, which is the body's way of fighting the infection, Vedantham noted. "This study was not designed to determine exactly what aspect of infection/inflammation led to DVT. This article should contribute to a major impetus to better delineate the pathophysiologic mechanisms which lead to DVT," he said.

Specifically, doctors need to determine what components of the inflammatory response can predispose someone to DVT and whether this process can be safely and effectively interrupted, Vedantham said. "For example, if there are routine blood tests we can perform to detect markers of inflammation and thereby identify which patients are at higher risk, then we might treat patients with prophylactic measures to prevent DVT. That would be the major future potential ramification of this line of study."

Another expert, Dr. Jack Ansell, a professor of medicine at Boston University School of Medicine, thinks there's not enough evidence yet to understand how DVT develops in patients. In addition, he believes that while doctors should be aware of the findings of this study, it shouldn't worry patients.

Infections are so common that if doctors made patients aware of this potential risk, it would cause more trouble than necessary, Ansell said. "The risk for a DVT from infection is so low, that, in general, people should not be concerned."

"It's too early to say what to do with these findings," he said. "It's way too early to treat patients prophylactically with an anticoagulant."

More information

The National Heart, Lung, and Blood Institute can tell you more about deep vein thrombosis.

SOURCES: Liam Smeeth, Ph.D., reader, clinical epidemiology, London School of Hygiene and Tropical Medicine, London; Suresh Vedantham, M.D., assistant professor, radiology and surgery, Washington University Medical School, St. Louis; Jack Ansell, M.D., professor, medicine, Boston University School of Medicine, Boston; April 1, 2006, The Lancet
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