ORBIT Bleeding Risk Score Components for Atrial Fibrillation
The ORBIT (Outcomes Registry for Better Informed Treatment of Atrial Fibrillation) Bleeding Risk Score consists of five key risk factors with specific point values: age ≥75 years (1 point), reduced hemoglobin/hematocrit/history of anemia (2 points), bleeding history (2 points), reduced renal function (1 point), and antiplatelet therapy use (1 point). 1
The Five Components of ORBIT Score
- O - Older age: Age ≥75 years (1 point) 1
- R - Reduced hemoglobin/hematocrit/history of anemia: (2 points) - This factor carries more weight than other factors in the score 1, 2
- B - Bleeding history: Previous bleeding events (2 points) - Also weighted more heavily in the scoring system 1, 2
- I - Insufficient kidney function: Reduced renal function (1 point) 1
- T - Treatment with antiplatelet drugs: Concomitant antiplatelet therapy (1 point) 1, 2
Risk Stratification Using ORBIT Score
The ORBIT score categorizes patients into three risk groups based on their total points:
- Low risk: 0-2 points (2.4% bleeding rate in derivation cohort) 1
- Intermediate risk: 3 points (4.7% bleeding rate) 1
- High risk: ≥4 points (8.1% bleeding rate) 1
Comparison with Other Bleeding Risk Scores
- The ORBIT score uses fewer variables (5) compared to other scores like HAS-BLED (9 variables) or HEMORR₂HAGES (12 variables), making it simpler to calculate at the bedside 1, 2
- Unlike HAS-BLED, the ORBIT score does not include labile INR, which makes it more applicable to patients taking direct oral anticoagulants (DOACs) 2, 3
- ORBIT and ATRIA scores have shown better predictive performance for major bleeding within the first 1100 days of DOAC treatment compared to other scores 3
Clinical Application
- The ORBIT score was specifically developed using data from the ORBIT-AF registry, which included a large community-based AF population taking oral anticoagulation 2
- It has demonstrated good discrimination ability with a C-index of 0.67 in the original validation cohort 2
- Some studies suggest ORBIT has better calibration than HAS-BLED and ATRIA when validated in external populations 2
Important Caveats
- While ORBIT may perform well in research settings, some real-world studies show that HAS-BLED may have higher sensitivity (62.8%) compared to ORBIT (37.1%) 4
- Recent data from the ESC-EHRA EORP-AF Registry suggests that ORBIT may have poorer calibration compared to HAS-BLED in NOAC-treated patients 5
- A high bleeding risk score should not automatically exclude patients from anticoagulation, as stroke prevention benefits often outweigh bleeding risks 6
- Regular reassessment of bleeding risk is essential as risk factors may change over time 6
Clinical Decision Making
- When using the ORBIT score, focus on identifying modifiable bleeding risk factors (anemia, renal function, antiplatelet therapy) that can be addressed to reduce bleeding risk 1
- For patients with high ORBIT scores (≥4), consider more frequent monitoring and follow-up rather than withholding anticoagulation 6
- Remember that the predictive value of all bleeding risk scores is modest (C-statistics typically around 0.6-0.7), highlighting the challenges in accurately predicting bleeding events 7, 4