Do compression stockings prevent blood clots? The jury is still out

A new study of compression stockings fails to settle the question of whether these garments reduce the risk of life-threatening blood clots after a stroke.

Dangerous clots in deep veins or the lungs are a common complication for patients who are bedridden after a stroke. Blood-thinning drugs do not completely prevent clots — and are unsafe for some patients — so doctors often prescribe compression stockings. In theory, they reduce clots by applying greater pressure at the ankle than higher up the leg, thus reducing the pooling of blood in deep veins.

The new study, led by United Kingdom researchers and involving 3,114 stroke patients in hospitals in nine countries, compared thigh-high compression stockings to knee-high ones.

Clots developed in 6.3 percent of thigh-high stocking wearers compared to 8.8 percent of knee-high wearers. (But encasing the whole leg also caused skin breaks in 4 percent of patients, compared to 3 percent for knee-high stocking wearers.)

While thigh-high stockings apparently cut clot risk by 30 percent, the results are confusing in light of a prior study in which the same research group found thigh-high stockings were no better than no stockings.

What does this mean? Perhaps knee-high stockings actually increase the risk of clots, the researchers say. More likely, the benefit of thigh-high stockings is so modest that it wasn’t detected in the previous study.

Another study is under way to compare no stockings with pneumatic compression devices, which intermittently inflate and deflate to promote circulation. But that still won’t clarify the effectiveness of compression stockings.

“Clinicians need to realize that despite the ubiquity of compression stockings, the net benefits and risks of this seemingly innocuous intervention remain uncertain,” concludes an editorial that accompanies  the study in the Nov. 2 issue of Annals of Internal Medicine.

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