For years, researchers have known that antiphospholipid antibodies (aPLs) can cause pregnancy loss and clotting, but they haven't known the true scope of the problem. Now a new study provides the first estimates of the prevalence of these antibodies in patients suffering from pregnancy loss, stroke, myocardial infarction, and deep vein thrombosis.

"Based on the available data, our best estimate is that around 10 to 15% of clotting disorders are associated with autoimmune antiphospholipid antibodies," said Doruk Erkan, M.D., an associate attending rheumatologist and clinician researcher at Hospital for Special Surgery in New York City, who is the senior researcher of the study.

The research will be presented on Nov. 13, at 3:15 p.m. ET, during the annual meeting of the American College of Rheumatology/Association of Rheumatology Health Professionals (ACR/ARHP), to be held Nov. 9-14, in Washington D.C.

In some individuals, aPLs do not cause any health problems, but in others, aPLs can trigger production of proteins that can cause inflammation and increase the risk for the formation of clots. This can cause pregnancy complications, strokes, heart attacks, and blood clots in other organs. Individuals who are aPL-positive and have either venous thrombosis, arterial thrombosis, or fetal loss are classified as having antiphospholipid syndrome (APS).

To get a grasp on the magnitude of the aPL problem, an international group of researchers searched PubMed to identify studies that involved patients with pregnancy loss, stroke, myocardial infarction or deep vein thrombosis, and that also tested patients for aPLs. They identified 108 papers and analyzed them for the type of outcome, the aPL tests used, the definition of positive aPL (low, medium, or high), confirmation of aPL, and the prevalence of positive aPL in the study population.

aPLs were found in 12% of individuals with a pregnancy loss, 14% of patients who had a stroke, 13% of patients who had a myocardial infarction, and 10% of patients who had deep vein thrombosis. Using databases that estimate the United States' prevalence of these conditions, the researchers extrapolated from their study data that aPLs are associated with approximately 60,000 cases of pregnancy loss, 120,000 cases of stroke, 120,000 cases of myocardial infarction, and 30,000 cases of deep vein thrombosis.

The researchers note that the estimates are limited by a lack of robust data. Many of the reports were old and didn't use the same classification criteria that are used today. In addition, the majority of the studies did not firmly establish the presence of aPLs in patients by performing two tests 12 weeks apart, something that is considered essential to confirm a diagnosis today. But despite the limitations, the new study does provide a rough snapshot of the prevalence of aPLs in patients with a number of health conditions.

"Accepting all of the limitations of the literature, the study does provide an estimate, which is important to raise awareness of aPLs and the health problems they cause. These numbers are also important for AntiPhospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) while designing clinical trials," said Dr Erkan, who is also the executive committee chair of the newly formed clinical research organization.

The study is a product of APS ACTION, which was created in November 2010 to facilitate the design of prospective, multicenter, multidisciplinary studies on APS. The alliance has created an international database for patients with positive aPLs. Because clinical manifestations of disease are rare events in aPL-positive individuals, the alliance is first aiming to follow 2,000 patients with persistently positive aPL for 10 years, with regular assessments, as well as data collection in the event of thrombosis. APS ACTION currently has 40 members from 28 centers around the world.

Other authors of the study are Michael Lockshin, M.D., from Hospital for Special Surgery; Laura Andreoli, M.D., from the University of Brescia, Brescia, Italy; Alessandra Banzato, M.D., from the University of Padua, Padua, Italy; Cecilia Chighizola, M.D., from the University of Milan, Milan, Italy; and Guillermo J. Pons-Estel, M.D., from the Hospital Clinic, Barcelona, Catalonia, Spain. All authors are members of APS ACTION (www.apsaction.org).