Risk of bleeding with blood thinners reduces over time

Blood thinners prescribed after blood clots in leg or lung initially increase the risk of bleeding, especially in women and elderly. But over time, this risk decreases and gender and age differences fade, a University of Gothenburg study shows.

The aim of the study, published in the Journal of Internal Medicine, was to investigate the increased risk of bleeding during treatment with anticoagulants after a blood clot in the leg or lung. While the treatment protects against further clots, it increases the risk of bleeding.

The standard protocol is to prescribe blood thinners for at least 3-6 months, also called initial treatment. After this time, the physician needs to decide whether to continue the treatment, which is called extended treatment. This decision entails weighing the risk of new blood clots if treatment is discontinued against the risk of bleeding if it is continued.

Common side effects of blood thinners include nosebleeds, blood in the urine, blood in the stools, and more frequent and larger bruises, all because the blood is not clotting as usual. The risk of bleeding is linked to the treatment itself, that is, a treatment-induced risk, as well as the patient's baseline risk, which is not always considered.

Initially increased risk of bleeding

Current knowledge in the field is mainly focused on the overall risk of bleeding, with older people being at greater risk. The extent of the treatment-induced bleeding risk in different groups and different treatment phases, on the other hand, has remained unknown.

The researchers used Swedish registry data encompassing more than 36,000 patients undergoing treatment with blood thinners after a blood clot in the leg or lung paired with an equal number of sex- and age-matched controls who had not had a clot and were not being treated with blood thinners.
During the first six months, 338 people (1.07 percent) in the patient group experienced bleeding compared to 103 people (0.29 percent) in the control group. The treatment-induced risk for women was higher than for men, and the oldest participants, aged 80 and above, were most at risk.

Diminished risk in the long run

During extended treatment, in the study from six months up to five years, the treatment-induced risk of larger bleeds was no longer associated with gender or older age. Overall, the treatment-induced risk decreased from just over 2 percent during initial treatment to 0.7 percent during extended treatment.
One of the driving forces behind the study is Katarina Glise Sandblad, a researcher at Sahlgrenska Academy at the University of Gothenburg as well as an internal medicine specialist at Sahlgrenska University Hospital.

"When I treat patients with blood clots, the decision whether to discontinue treatment after the initial phase or to continue with lifelong treatment can be difficult. This study shows that the share of the bleeding risk due to blood thinners is low during extended treatment and doesn't seem to increase with age. This is reassuring for both me and my patients," she says.