Positive family history a risk for venous thrombosis

FAMILY history may be more important in the assessment of risk for venous thrombosis than either thrombophilia testing or genetic testing.

Dutch researchers compared the impact of family history, genetic risk factors, and environmental triggers collected from 1605 patients who had a first venous thrombosis of the leg or pulmonary embolism, with 2159 age- and sex-matched controls.

A positive family history (at least one first-degree relative had experienced venous thrombosis) was associated with a more than two-fold increased risk of venous thrombosis.

The risk increased to four-fold for those patients with more than one affected relative.

“A young age of the affected relative and, in particular, the number of affected relatives more strongly indicated a predisposition to develop venous thrombosis,” the authors said.

However, they were surprised that family history had a poor predictive value and sensitivity as a test for genetic factors. They said this “either implies the existence of unknown genetic risk factors or clustering through household effects”.

Professor Alexander Gallus, professor of haematology at Flinders University school of medicine, Adelaide, said: “Most of the people [in the study cohort] with a family history... and thrombosis actually did not have a genetic predisposition, so we’ve still got a lot to learn.”

Associate Professor Ross Baker, a consultant haematologist at Royal Perth Hospital in WA, said GPs should initially assess a patient’s family history and, if positive, genetic tests could be undertaken.

“The laboratory testing for all these genetic factors is useful if you find things, but again the history seems more important,” he said.

Arch Intern Med 2009; 169:610-15.