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Summaries for Patients are a service provided by Annals to help patients better understand the complicated and often mystifying language of modern medicine.
SUMMARIES FOR PATIENTS
Blood Clots in People with Factor V Leiden Mutation
2 March 2004 | Volume 140 Issue 5 | Page I-50
Summaries for Patients are presented for informational purposes only. These summaries are not a substitute for advice from your own medical provider. If you have questions about this material, or need medical advice about your own health or situation, please contact your physician. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the American College of Physicians.
The summary below is from the full report titled "Factor V Leiden and the Risk for Venous Thromboembolism in the Adult Danish Population." It is in the 2 March 2004 issue of Annals of Internal Medicine (volume 140, pages 330-337). The authors are K. Juul, A. Tybjærg-Hansen, P. Schnohr, and B.G. Nordestgaard.
What is the problem and what is known about it so far?
Blood clots sometimes occur in deep veins in the legs. Pieces of these clots, known as emboli, can break off and travel through the bloodstream, blocking arteries in the lungs. The blood clots and emboli can cause serious symptoms and death. Surgery, pregnancy, trauma, hormone therapy, and inherited blood disorders increase risks for blood clots and emboli. Factor V Leiden is one of these inherited disorders. Some studies show that it is associated with very high risks for clots. However, many researchers wonder about the actual size or amount of risks for clots and emboli among people with the defect.
Why did the researchers do this particular study?
To find out how often blood clots and emboli occur in people with the factor V Leiden mutation.
Who was studied?
9253 randomly selected adults from Denmark who were tested for factor V Leiden.
How was the study done?
Researchers asked participants about their medical history and lifestyle, gave them physical examinations, and took blood samples. They divided the participants into 3 groups based on whether they had no factor V Leiden mutations, had a single form (allele) of the factor V Leiden gene (heterozygote), or had a double form of the gene (homozygote). They followed everyone for up to 23 years to see who got clots or emboli. They used hospital records and national databases of hospital discharges and deaths to confirm diagnoses. They then calculated the risk for getting clots for each of the 3 groups. They also examined whether people with certain characteristics, such as obesity and older age, had higher risks for clots.
What did the researchers find?
Heterozygotes and homozygotes for factor V Leiden had about 3 and 18 times higher risks for clots and emboli than people without factor V Leiden mutations. The risks for clots and emboli over a 10-year period were about 1% among heterozygote people and 3% among homozygote people who did not smoke, were not overweight, and were younger than 40 years of age. The risks over a 10-year period were 10% in heterozygote people and 51% in homozygote people who smoked, were overweight, and were over 60 years of age.
What were the limitations of the study?
The researchers did not know whether any of the participants were taking blood thinners that might decrease risks for blood clots.
What are the implications of the study?
Blood clots and emboli associated with factor V Leiden mutations are important, but the risks for them are lower than previously reported.
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