Why use it

Identifies patients unlikely to achieve stable anticoagulation on warfarin, supporting the decision to prescribe a DOAC. Most current AF guidelines (ESC 2020) recommend using SAMe-TT₂R₂ to guide anticoagulant selection when both options are clinically appropriate.

About

The SAMe-TT₂R₂ score predicts the likelihood that a patient with atrial fibrillation will achieve a good time-in-therapeutic-range (TTR ≥ 65%) on vitamin K antagonist (VKA/warfarin) therapy. Patients with a score ≥ 2 are less likely to achieve stable anticoagulation on warfarin and may be better candidates for direct-acting oral anticoagulants (DOACs). The acronym encodes: Sex (female), Age (<60), Medical history (2 or more comorbidities), Treatment (interacting medications), Tobacco use (×2), Race/ethnicity (non-white, ×2). It was derived from the Euro Heart Survey on AF and validated in multiple international cohorts.

When to use

Newly diagnosed non-valvular atrial fibrillation requiring anticoagulation
Re-evaluation of anticoagulation strategy in patients with poor INR control on warfarin
Deciding between DOAC and warfarin when both are clinically appropriate
Patients in regions where DOACs are not available or cost-prohibitive (TTR management)

Formula

S = Sex (female): +1 A = Age (<60 years): +1 Me = Medical history (≥ 2 of: HTN, DM, CAD/MI, PAD, CHF, previous stroke, pulmonary disease, hepatic/renal disease): +1 T = Treatment (drugs interacting with warfarin: antiplatelets, NSAIDs, amiodarone): +1 T₂ = Tobacco use within 2 years: +2 R₂ = Race (non-Caucasian/non-white): +2 Total: 0–8 Score 0–1: Low risk (good TTR predicted on warfarin) Score ≥ 2: High risk (poor TTR predicted → prefer DOAC)

Pearls & pitfalls

Score ≥ 2 indicates ≥ 60% probability of poor INR control (TTR < 65%) on warfarin.
Female sex adds only +1, while tobacco use and non-Caucasian race each add +2 — these are the most impactful variables.
Medical history counts comorbidities from a defined list; ≥ 2 is required for 1 point.
Treatment refers to interacting drugs: antiplatelets, NSAIDs, or other cytochrome P450-interacting medications.
In the Euro Heart Survey derivation cohort, a score ≥ 2 had a negative predictive value of 72% for good TTR.
This score helps stratify patients BEFORE starting anticoagulation — it is a predictive tool, not a monitoring tool.
In patients already on warfarin with measured TTR < 65%, consider switching to a DOAC without using this score.
DOACs are contraindicated in mechanical heart valves and moderate-to-severe mitral stenosis — use warfarin in these patients regardless of score.

Next steps

Score 0–1: Good candidate for warfarin with expected high TTR; DOAC remains a valid alternative. Score ≥ 2: Poor predicted TTR — DOAC preferred (apixaban, rivaroxaban, dabigatran, edoxaban) if no contraindication. For patients already on warfarin with poor INR control, consider switching to a DOAC regardless of score. Always assess renal function, bleeding risk (HAS-BLED), and stroke risk (CHA₂DS₂-VASc) concurrently.

Evidence

Apostolakis S et al. Factors affecting quality of anticoagulation control among patients with atrial fibrillation on warfarin: the SAMe-TT₂R₂ score. Chest. 2013;144(5):1555-1563. Validated in AFFIRM trial data and the FANTASIIA registry. Endorsed by ESC 2020 AF Guidelines (Class IIa, Level B).

References

Apostolakis S et al. Factors affecting quality of anticoagulation control among patients with atrial fibrillation on warfarin: the SAMe-TT₂R₂ score. Chest. 2013;144(5):1555-1563. — link
Hindricks G et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation. Eur Heart J. 2021;42(5):373-498. — link
Roldan V et al. The SAMe-TT₂R₂ score predicts poor anticoagulation control in AF patients. Am J Med. 2013;126(11):e1-e6. — link

SAMe-TT₂R₂ Score (DOAC vs. Warfarin)

Calculator