Venous thromboembolism risk among hospitalized patients

July 13, 2007

Venous thrombosis (VTE), the formation of blood clots in a vein, is a major health problem for hospitalized patients in the United States. In the short term, VTE can lead to deep vein thrombosis (DVT), typically in the legs, and pulmonary embolism (PE), which occurs when a piece of the blood clot migrates into an artery of the lungs. Evidence implicates PE in up to 10 percent of sudden in-hospital deaths. In the long term, VTE can lead to post-thrombotic syndrome (PTS), marked by persistent leg pain, swelling, and cramps, or pulmonary hypertension. Fortunately, such dire complications are easy to avoid through preventive strategies, from compression boots to anti-clotting medications. Unfortunately, inpatients at risk for VTE are routinely overlooked.

To provide a clear, quantitative sense of the scope of this problem, researchers at the University of Massachusetts Medical School and Mayo Clinic College of Medicine set out to estimate the total number of US inpatients at risk for VTE - a crucial figure previously unknown. Their results, which will be published online in the American Journal of Hematology (, strongly support the need for reinforcing established national guidelines for identifying patients at risk for VTE, as well as monitoring compliance with hospital protocols for VTE prevention.

"Our findings suggest that each year, almost one-third of hospitalized patients are at risk of VTE," notes the study's lead author, Dr. Frederick Anderson. "This highlights the magnitude of the US public health risk posed by this potentially preventable condition."

To determine the number of hospitalized patients at "substantial risk" for developing VTE, Dr. Anderson and his colleagues used criteria defined by the American College of Chest Physicians (ACCP) - widely respected guidelines that have been available to physicians across the country for 15 years. They applied them to the Nationwide Inpatient Sample (NIS), the largest all-payer inpatient care database in the US, containing information on over 8 million hospital stays, for 2003. That year, an estimated 38,220,659 patients were discharged from roughly 6,000 acute-care hospitals. 56 percent of these patients (21, 574, 294 individuals) met the study's inclusion criteria for age and length of hospital stay: two days or more, sufficient time to diagnose and prescribe VTE prevention. Of the study population, 20 percent (7,786,390 individuals) were surgical patients ages 18 and older, and 40 percent (15,161,586 individuals) were patients ages 40 and older hospitalized for a serious medical condition.

When the ACCP criteria for VTE risk were applied to the surgical patients, 44 percent were considered low risk and would not have been candidates for preventative measures.

However, 15 percent were at moderate risk, 24 percent were at high risk, and 17 percent were at extreme risk of VTE, due to a combination of age, other medical conditions, type of surgery, and prior history of blood clots. In the group hospitalized for reasons other than surgery, 51 percent met the ACCP criteria for VTE risk based on the nature of their illness: heart failure, respiratory failure, pneumonia, cancer, acute myocardial infarction, stroke, trauma, and sepsis among them.

In total, more than 12 million of the approximately 38 million patients discharged from US hospitals in 2003 were at risk of VTE during their hospital stay based on the standard ACCP criteria. From their data, the researchers were unable to gauge what proportion of this staggering number of at-risk patients benefited from therapeutic intervention. Yet, based on numerous reports, Dr. Anderson and his associates speculate that at least half of hospitalized patients at risk for VTE receive no preventative care, and countless suffer the consequence of serious complications, including premature death.

Samuel Z. Goldhaber, MD, Professor of Medicine at Harvard and a cardiovascular specialist with Brigham and Women's Hospital, notes this study's significant contribution toward raising VTE awareness and improving intervention for hospitalized patients. Still, improving inpatient care is only the first step. "VTE risk does not simply evaporate when patients are discharged from hospitals," Dr. Goldhaber drives home, stressing the need to keep outpatients informed of VTE risk, and committed to exercising regularly and following their doctor's prescriptions for preventive measures. "Anderson and his group have defined a broad 'base of the iceberg' of danger," he observes. "However, the fundamental problem is even more profound and goes beyond the millions of hospitalized patients annually that they have identified."
Article: "Estimated Annual Numbers of US Acute-care Hospital Patients at Risk for Venous Thromboembolism," Frederick Anderson, Max Zayaruzny, John Heit, Dogan Fidan, and Alexander Cohen; American Journal of Hematology, July 2007; (DOI: 10.1002/ajh.20983).

Editorial: "Venous Thromboembolism Risk Among Hospitalized Patients: Magnitude of the Risk Is Staggering," Samuel Z. Goldhaber, MD; American Journal of Hematology, July 2007; (DOI: 10.1002/ajh.20997).


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