How to Calculate the Mayo Surgical Risk Score
The Mayo Clinic Risk Score (MCRS) is calculated using seven preprocedure variables to predict in-hospital mortality for patients undergoing cardiac procedures, particularly percutaneous coronary interventions (PCI) and coronary artery bypass graft (CABG) surgery.
Components of the Mayo Clinic Risk Score
The MCRS uses the following seven variables to calculate surgical risk:
- Age
- Creatinine level
- Ejection fraction
- Myocardial infarction ≤24 hours before procedure
- Presence of cardiogenic shock
- Presence of congestive heart failure
- Peripheral vascular disease
Risk Score Calculation
The score is calculated by assigning points to each variable and summing them to create an integer-based risk score. The total score ranges from 0 to approximately 24, with higher scores indicating higher risk 1.
Risk Stratification Categories
Based on the total MCRS, patients are classified into five risk categories:
- Very low risk: MCRS < 5
- Low risk: MCRS 6-8
- Moderate risk: MCRS 9-11
- High risk: MCRS 12-14
- Very high risk: MCRS 15-25
Mortality Prediction
The MCRS has demonstrated strong association with observed mortality:
- Very low risk (MCRS < 5): 0% mortality
- Low risk (MCRS 6-8): 0.9% mortality
- Moderate risk (MCRS 9-11): 3.2% mortality
- High risk (MCRS 12-14): 10.7% mortality
- Very high risk (MCRS 15-25): 25.1% mortality 2
Validation and Performance
The MCRS has been validated in multiple studies:
- It shows excellent discriminatory ability with a c-statistic of 0.76-0.85 for predicting in-hospital mortality 2, 3
- It has been validated in external populations including the National Heart, Lung, and Blood Institute Dynamic Registry 3
- It has been shown to predict mortality accurately across various cardiac procedures, including both PCI and CABG 1
Clinical Applications
The MCRS is particularly valuable for:
- Providing patients with individualized, evidence-based estimates of procedural risk
- Informing the informed consent process before cardiac revascularization
- Comparing risk between percutaneous and surgical revascularization options 1
Limitations
- The MCRS was primarily developed for cardiac procedures and may not be as accurate for other surgical specialties
- Some studies have shown it may overestimate mortality in certain populations, particularly for long-term (1-year) outcomes 4
- The model's performance may vary across different healthcare systems and patient populations
Comparison with Other Risk Models
While the MCRS performs well, it's worth noting that specialized risk calculators like the American College of Surgeons NSQIP Surgical Risk Calculator may provide more comprehensive risk assessment for non-cardiac surgeries, with superior discriminative power for general surgical procedures 5.
For cardiac procedures specifically, the MCRS provides a simple, validated tool that requires only seven readily available clinical variables to generate meaningful risk predictions for patient counseling and clinical decision-making.