Women with an unexplained DVT or PE and HERDOO2 score of ≥ 2 have a high risk of developing a new DVT or PE and should consider remaining on anticoagulation.
Women with an unexplained DVT or PE and HERDOO2 score of 0 or 1 have a low risk of developing a new DVT or PE and can be offered the option of stopping anticoagulation after a minimum of 5 months of treatment.
All men with an unexplained DVT or PE are at high risk of developing a new DVT or PE therefore they should consider remaining on anticoagulation.
Understanding the problem
Anticoagulants protect people who have deep vein thrombosis or pulmonary embolism from forming new blood clots while their body works on breaking down the old blood clots. How long people with DVT or PE should take an anticoagulant is not based on when the clot is gone. Instead, it is based on when the risk factor that caused the blood clot is gone.
For example, Alice develops a DVT one week after hip replacement surgery. She is treated with anticoagulants for 3 months, and then her doctor tells her she can stop taking them. Alice's risk factor for DVT was surgery.
For many people, the risk factor that caused their DVT or PE is either weak (e.g., travel) or unknown. These people remain at risk for forming new blood clots for the rest of their lives. Some people will decide to continue taking anticoagulants indefinitely to reduce their risk. However, some people will choose to stop.
Scores or checklists have been developed to help doctors guide people with unexplained clots who are undecided about whether they should continue or stop anticoagulant treatment. The study described below was performed to find out if one checklist (HERDOO2) is helpful for identifying women who can safely stop anticoagulants after 5 to 12 months of anticoagulation.
Who? This study included 2,747 adults (average age 54; 44% female) who had their first unexplained DVT or PE, had completed 5 to 12 months of anticoagulation, and were undecided about whether to continue or stop anticoagulant treatment.
What? This study used the HERDOO2 score to estimate the risk of having a new blood clot.
H: Hyperpigmentation (brown discolouration around ankle or shin) of either leg
E: Edema (swelling) of either leg
1 point (if any present)
|D: D-dimer (positive blood test while on anticoagulation)||1 point|
|O: Obesity (BMI > 30 kg/m2)||1 point|
|O: Older (age > 65 years)||1 point|
Interpretation of Score:
Score ≥2: high risk of new DVT or PE (should continue anticoagulation)
Score 0 or 1: low risk of DVT or PE (may discontinue anticoagulation)
All men have a high risk of new DVT or PE (should continue anticoagulation)
Risk of developing new DVT or PE in the first year after an unexplained DVT or PE treated for 5 to 12 months
Risk classification based on HERDOO2 score
Number of people (% of study population)
New DVT or PE rate at 1 year
Women at high risk (score ≥ 2) and all men
About 2 out of 100 people had a new DVT or PE while taking anticoagulants
About 8 out of 100 people had a new DVT or PE while off of anticoagulants
Women at low risk (score 0 or 1)
About 3 out of 100 people had a new DVT or PE while off of anticoagulants
None had a new DVT or PE while taking anticoagulants
This Evidence Summary is based on the following article:
Rodger MA, Le Gal G, Anderson DR, et al. Validating the HERDOO2 rule to guide treatment duration for women with unprovoked venous thrombosis: multinational prospective cohort management study. BMJ. 2017 Mar 17;356:j1065. PubMed
Lori-Ann Linkins, MD, MSc (Clin Epi), FRCPC
Dr. Linkins is an Associate Professor of Medicine (thrombosis) at McMaster University in Hamilton, Canada. She holds a Masters Degree in Health Research Methodology and is a Deputy Editor with the Health Information Research Unit, McMaster. She is Co-Editor of the ACP Journal Club and Co-lead on the CanVECTOR Knowledge Translation Platform.
Published: Friday, May 18, 2018
Last Updated: Thursday, July 30, 2020