A new clinical decision rule (CDR) offers clinicians clues on when to stop anticoagulation therapy in women who had a first, unprovoked venous thromboembolism (VTE), data from the REVERSE II* study, reported at the ESC Congress 2016, have shown.

Current guidelines are unclear on the duration of anticoagulation after a first unprovoked VTE. Some recommend life-long treatment after a single VTE episode while others recommend 6 months of anticoagulation.

“It is a very difficult decision whether to continue blood thinners for life or [to] stop in patients who had an unprovoked VTE,” said lead author Dr Marc Rodger from the Ottawa Hospital and University of Ottawa in Ottawa, Ontario, Canada. “To have a simple tool that can identify low-risk group makes it much more comfortable for both clinicians and patients.”

In the REVERSE II study, Rodger and his team tested the validity of the HERDOO2 CDR in 2,779 patients with a first, unprovoked VTE who had completed 5–12 months of anticoagulant therapy. [ESC 2016 Congress, abstract 5721]

HERDOO2 stands for four risk factors – hyperpigmentation, edema or redness in either leg (HER), d-dimer assessed through blood testing (D), obesity (O=BMI ≥30 kg/m²), and older age (O=≥65 years). A score of 0–1 means an individual has a low risk of recurrent VTE, 2–4 means high risk.

Men and women who were found to be at high risk of recurrent VTE continued with their anticoagulant therapy whereas a majority of the 622 women who were identified to be at low risk stopped taking anticoagulants.

After a year of follow-up, VTE rate was 3 percent per 100 patient-years in low-risk women who had stopped taking anticoagulants versus 8.1 percent per 100 patient-years in high-risk patients who had continued with their anticoagulant therapy.  

“Women with 0–1 HERDOO2 points had low risk of recurrence, and were able to safely discontinue blood thinners,” said Rodger.

In a derivation study done by Rodger and colleagues in 2008, men and women with 2–4 HERDOO2 points had a 14 percent risk of recurrent VTE in the year after stopping anticoagulants whereas women with 0–1 HERDOO2 points had a 1.6 percent risk of recurrent VTE, suggesting that the HERDOO2 rule only applies to women. [CMAJ 2008; 179:417-426]

“The HERDOO2 rule is the only currently validated CDR to assist clinicians, patients and policy-makers to decide who can discontinue anticoagulants after an unprovoked VTE,”  Rodger said. “This is an important finding because 50 percent of women with unprovoked blood clots can be spared the burden, the costs and the risks of life-long anticoagulation.”

Rodgers said some questions remain unanswered though, for example, whether indefinite anticoagulation is required for men and women at high risk of recurrent VTE, which is not the subject of the study, and the duration of treatment for postmenopausal women aged 50 and older who may be at low risk for VTE but had a higher than expected recurrent VTE rate of 5.7 percent in the study.

Given this finding, further validation of the HERDOO2 rule may be warranted in this subset of postmenopausal women, he added.