What are the limitations of the herdoo2 rule?

While the herdoo2 rule is highly validated, it should not replace clinical judgment. OpiCalc provides the latest evidence-based limitations for the herdoo2 rule to ensure safe bedside use and optimal diagnostic accuracy.

How does the herdoo2 rule compare to other Hematology scores?

The herdoo2 rule is a gold-standard diagnostic tool. OpiCalc provides side-by-side clinical guidance to help clinicians choose the most specific evidence-based tool for their patient's presentation.

Is the herdoo2 rule free to use?

Yes. OpiCalc provides the herdoo2 rule completely ad-free and optimized for mobile bedside use, ensuring you can calculate medical risk swiftly and without distraction.

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HERDOO2 Rule

VTE Recurrence (HERDOO2): Validated rule to identify low-risk women. Men with unprovoked VTE are inherently high-risk and are not eligible for rule-out.

1. Biological Sex

2. HERDOO2 Points (1 pt each)

Recurrence Risk Result

Low Risk

Management Insight

Consider Stopping Anticoagulation

Recurrence rate < 2% per year. Safe to discontinue therapy.

Guidelines & Evidence

Clinical Details

Section 1

When to Use

Identifying women with a first unprovoked Venous Thromboembolism (VTE) who have a low risk of recurrence.

Deciding whether anticoagulation can be safely discontinued after the initial 3-6 month treatment period.

The 'Males Always High' Rule

The HERDOO2 rule is only applicable to women. Men with unprovoked VTE are considered high-risk for recurrence (regardless of these points) and usually require indefinite anticoagulation.

Section 2

Formula & Logic

Point Allocation (1 pt each)

Post-thrombotic signs: Hyperpigmentation, Edema, or Redness in either leg.

Renal insufficiency: Creatinine Clearance < 50 mL/min.

D-dimer: ≥ 250 µg/L (drawn while on anticoagulation).

Obesity: BMI ≥ 30 kg/m².

Older age: Age ≥ 65 years.

Risk Stratification (Women Only)

Score	Risk Class	Recurrence Rate
0 - 1	Low Risk	~1.6% per year (Safe to stop)
≥ 2	High Risk	> 8% per year (Continue VKA/DOAC)

Section 3

Pearls/Pitfalls

Unprovoked Pivot

The biggest challenge in thrombosis is deciding who needs lifelong therapy. HERDOO2 provide a validated escape-clause for roughly 50% of women with unprovoked events, sparing them the risk and cost of long-term DOAC therapy.

Section 4

Evidence Appraisal

Primary Strategy

Identifying unprovoked venous thromboembolism patients at low risk for recurrence who can discontinue anticoagulant therapy.

Rodger MA et al. • CMAJ. 2008;179(5):417-26.

View Source

Validating the HERDOO2 rule to guide discontinuation of anticoagulation.

Rodger MA et al. • BMJ. 2017;Prospective validation in a large global cohort.

View Source

Section 5

Literature

Acronym

HERDOO2 stands for: Hyperpigmentation, Edema, or Redness (HE); Renal insufficiency (R); D-dimer (D); Obesity (O); Old age (O).

Last Comprehensive Review: 2026

Related Hematology Tools

Mixing Study Interpretation

Age-adjusted D-dimer Threshold

sPESI

HEP Score

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