For healthcare professionals
HERDOO2 rule calculator
The HERDOO2 rule counts four factors in women who have had a first unprovoked venous thromboembolism (VTE), a deep vein thrombosis or pulmonary embolism, to find those at low risk of a new clot if anticoagulation stops. This tool is written for clinicians and is not a diagnosis.
Patient details
For a first unprovoked VTE, measured while still on anticoagulation. Nothing you enter leaves this page.
What you will see
The HERDOO2 score from 0 to 4, its risk group and the point for each factor.
Educational only, not medical advice. Never start, stop or skip a blood thinner on your own.
Source
The HERDOO2 rule by Rodger MA and colleagues, CMAJ 2008 (derivation) and BMJ 2017 (validation), both cited, not quoted. The items, thresholds and groups are as printed in the open access Table 4 of Weitz and colleagues, TH Open 2020 (CC BY), and Table 1 of Stevens and colleagues, J Clin Med 2020 (CC BY). The yearly recurrence figures are from Table 1 of Stevens and colleagues. The tests check each item, the maximum of 4, the low group of 0 or 1 and the edges at D-dimer 250, BMI 30 and age 65.
Validated in
Adults with a first unprovoked VTE after 5 to 12 months of anticoagulation, as summarized by Stevens and colleagues; the index event was a proximal deep vein thrombosis or a pulmonary embolism (Ensor and colleagues 2016). Weitz and colleagues note that the rule applies to women only and has been applied only to unprovoked VTE and to women with estrogen-associated VTE.
Limits
Women only: no low-risk group of men was found. Not for VTE provoked by surgery, trauma or cancer. The D-dimer is measured while the patient is still on anticoagulation, and D-dimer assays differ; the original papers name the assays used. A 2016 systematic review (Ensor and colleagues, BMJ Open) rated the HERDOO2 derivation at high risk of bias, citing methodological issues such as underpowered analyses and data-driven categorisation of predictors, and noted that none of the models it reviewed had been externally validated; the 2017 BMJ study is that prospective validation. The rates shown are from the derivation study as summarized by Stevens and colleagues, not from the validation study, and are group averages, not a personal prediction. D-dimer 250, BMI 30 and age 65 count (each item is 'or more').
The four items
HERDOO2 items, as printed by Weitz and colleagues 2020, Table 4 (Weitz 2020) (Rodger 2008), one point each (Stevens 2020):
- Hyperpigmentation, Edema or Redness of either leg (signs of post-thrombotic syndrome): 1
- D-dimer of 250 µg/L or more before stopping anticoagulation: 1
- Obesity, body mass index 30 kg/m² or more: 1
- Older age, 65 years or more: 1
The maximum is 4. The name adds a 2 because there are two "O" items.
Worked example: a 58-year-old woman with a BMI of 32 (1), a D-dimer of 180 µg/L on treatment (0) and no leg signs (0) scores 1, the low risk group.
Risk groups
Women with 0 or 1 item are the low risk group, and women with 2 or more are the high risk group (Stevens 2020) (Weitz 2020). In the derivation study, as summarized by Stevens and colleagues in Table 1, the yearly recurrence risk was (Stevens 2020):
- Low risk women (0 or 1 item): 1.6% per year
- High risk women (2 or more items): 14.1% per year
- Men (no low risk group found): 13.7% per year
Weitz and colleagues print a yearly recurrence of 1.3 to 1.6% for women with a low score (Weitz 2020). The rule was then tested prospectively by Rodger and colleagues in 2017, where low risk women stopped anticoagulation (Rodger 2017); the rates from that study are in the original paper.
Reading the result
Weitz and colleagues describe the rule this way: men with unprovoked VTE should continue anticoagulation, while women with a score of 2 or more should continue (Weitz 2020). Ensor and colleagues point out that the rule gives a split at an annual recurrence risk under 3% rather than a personal risk at set time points (Ensor 2016). A low score is one input in the choice about stopping treatment, alongside bleeding risk and the patient's own view.
General safety advice (not part of the rule): new leg swelling or pain, sudden shortness of breath or chest pain after stopping a blood thinner needs urgent care. Never stop, skip or change a blood thinner because of a score. Talk to the clinician who prescribes it.
Related tools
For men and women after a first unprovoked clot, the DASH score estimates the yearly risk of a new clot once anticoagulation has stopped. For a suspected new clot, see the Wells score for DVT and the Wells score for PE. For bleeding risk while on a blood thinner for a clot, see the VTE-BLEED score, and to check weight first, the BMI calculator. Other bedside scores are listed under For healthcare professionals.
Sources
- Weitz JI, Prandoni P, Verhamme P. Anticoagulation for patients with venous thromboembolism: when is extended treatment required? TH Open. 2020;4(4):e446-e456. doi:10.1055/s-0040-1721735. PMID 33376944. Open access (CC BY). Table 4 (HERDOO2 items, women only, low score of 1 or less). pmc.ncbi.nlm.nih.gov/articles/PMC7758152/
- Stevens H, Peter K, Tran H, McFadyen J. Predicting the risk of recurrent venous thromboembolism: current challenges and future opportunities. J Clin Med. 2020;9(5):1582. doi:10.3390/jcm9051582. PMID 32456008. Open access (CC BY). Table 1 (HERDOO2 inclusion, groups and annualised recurrence risk). pmc.ncbi.nlm.nih.gov/articles/PMC7290951/
- Ensor J, Riley RD, Moore D, Snell KI, Bayliss S, Fitzmaurice D. Systematic review of prognostic models for recurrent venous thromboembolism (VTE) post-treatment of first unprovoked VTE. BMJ Open. 2016;6(5):e011190. doi:10.1136/bmjopen-2016-011190. PMID 27154483. Open access (CC BY). pmc.ncbi.nlm.nih.gov/articles/PMC4861103/
- Rodger MA, Kahn SR, Wells PS, Anderson DA, Chagnon I, Le Gal G, et al. Identifying unprovoked thromboembolism patients at low risk for recurrence who can discontinue anticoagulant therapy. CMAJ. 2008;179(5):417-426. doi:10.1503/cmaj.080493. PMID 18725614. Cited, not quoted. doi.org/10.1503/cmaj.080493
- Rodger MA, Le Gal G, Anderson DR, Schmidt J, Pernod G, Kahn SR, et al.; REVERSE II Study Investigators. Validating the HERDOO2 rule to guide treatment duration for women with unprovoked venous thrombosis: multinational prospective cohort management study. BMJ. 2017;356:j1065. doi:10.1136/bmj.j1065. PMID 28314711. Cited, not quoted. doi.org/10.1136/bmj.j1065
Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-11-03. Spotted an error? See About.