What Is the STS Risk Score?
If you or a loved one is facing heart surgery, your surgeon has almost certainly calculated something called an STS risk score. It is the most widely used surgical risk prediction tool in cardiac surgery — and understanding it can help you make a more informed decision about your care.
The STS PROM (Predicted Risk of Mortality) is a statistical model developed by the Society of Thoracic Surgeons, a professional organization representing more than 7,700 cardiothoracic surgeons worldwide. First introduced in 1989 and continuously refined with data from millions of cardiac surgery cases, the STS score estimates your individual risk of mortality and major complications after heart surgery.
At WhiteGloveMD, we believe every patient deserves to understand their risk profile before making surgical decisions. You can explore your estimated risk using our STS Risk Calculator.
What Variables Does the STS Score Use?
The STS risk model incorporates dozens of clinical variables. These fall into several major categories:
Patient Demographics
- Age — Risk increases with each decade, particularly after age 70
- Sex — Female patients carry modestly higher surgical risk for certain procedures
- Body surface area (BSA) — Extremes of body size affect surgical outcomes
Cardiac Function
- Ejection fraction (EF) — How well your heart pumps. An EF below 40% significantly increases risk
- Heart failure symptoms — NYHA functional class (I through IV)
- Previous cardiac surgery — Reoperations carry higher risk due to scar tissue
- Recent heart attack — Timing relative to surgery matters enormously
Comorbidities
- Diabetes — Especially insulin-dependent diabetes
- Chronic lung disease — Severity graded as mild, moderate, or severe
- Peripheral vascular disease — Indicates widespread arterial disease
- Cerebrovascular disease — Prior stroke or TIA
- Renal function — Creatinine level and dialysis status are powerful risk predictors
Procedural Factors
- Surgical urgency — Elective, urgent, emergent, or salvage
- Procedure type — Isolated CABG, isolated valve, combined procedures
- Number of diseased vessels — For coronary artery bypass surgery
Each variable is weighted according to its statistical impact on outcomes. The model then produces a personalized risk estimate. Try our risk calculator to see how these factors apply to your situation.
How to Interpret Your STS Score
Your STS PROM is expressed as a percentage — your estimated risk of dying within 30 days of surgery, or during the same hospitalization. Here is how cardiac surgeons generally categorize these scores:
Low Risk: STS Score Below 4%
Most patients undergoing elective cardiac surgery fall into this category. An STS score of 1–2% means that out of 100 similar patients having the same operation, 98–99 are expected to survive the perioperative period. Surgery is generally considered a safe and appropriate option for these patients.
Intermediate Risk: STS Score 4–8%
At this level, the risk is meaningful but surgery may still be the best option. This is where the Heart Team discussion becomes critical. For aortic valve disease, patients in this range may be candidates for either traditional surgery (SAVR) or transcatheter aortic valve replacement (TAVR).
High Risk: STS Score Above 8%
These patients face substantial surgical risk. Alternative approaches — such as TAVR for aortic stenosis, or optimized medical therapy — should be seriously considered. Patients with STS scores above 15% are sometimes classified as extreme risk or prohibitive risk, meaning the expected surgical mortality may outweigh the potential benefit.
Your score is not a verdict. It is a starting point for a conversation with your Heart Team. If you have questions about what your score means, our physicians are available for a cardiac second opinion.
What Do STS Star Ratings Mean for Hospitals?
The STS also publishes star ratings for cardiac surgery programs across the United States. These ratings (one, two, or three stars) compare a hospital's actual surgical outcomes against what would be expected given the risk profiles of their patients.
- Three stars — Performance significantly better than expected
- Two stars — Performance within the expected range
- One star — Performance below what would be expected
Star ratings account for patient complexity. A hospital that operates on very sick patients and still achieves good outcomes will earn three stars. These ratings are publicly available and are one of the most reliable ways to evaluate a cardiac surgery program.
How the STS Score Is Used in Heart Team Conferences
Modern cardiac care relies on a Heart Team approach — a multidisciplinary conference where cardiac surgeons, interventional cardiologists, imaging specialists, and anesthesiologists review each patient's case together.
The STS score is the foundation of this discussion. It helps the team answer critical questions:
- Is the patient a candidate for surgery, or should a less invasive approach be considered?
- If surgery is appropriate, what is the expected risk?
- Are there modifiable risk factors (such as stopping smoking or optimizing kidney function) that could lower the score before surgery?
- Does the patient's risk profile suggest they need a high-volume, specialized center?
WhiteGloveMD's second opinion process includes a full Heart Team-style review. Our physicians independently calculate your STS score, verify the inputs, and determine whether the recommended treatment plan is appropriate for your risk level.
Why You Should Always Ask for Your Score
Many patients go through surgical consultations without ever hearing their STS score. This is a missed opportunity. Here is why you should ask:
- It is your data. The score is calculated from your medical information. You have every right to know it.
- It enables comparison. If you are seeking a second opinion, knowing your STS score allows the consulting physician to quickly understand your risk profile.
- It reveals alternatives. A high STS score may qualify you for less invasive procedures (like TAVR) that your initial surgeon did not mention.
- It sets expectations. Understanding your risk helps you prepare mentally and practically for surgery and recovery.
When you request a second opinion through WhiteGloveMD, we calculate your STS score independently and explain it to you in plain language.
Limitations of the STS Score
No risk model is perfect. The STS score has known limitations:
- Frailty — The model does not directly measure frailty, which is a major predictor of surgical outcomes in elderly patients
- Liver disease — Hepatic dysfunction is underrepresented in the model
- Porcelain aorta — A heavily calcified aorta increases surgical risk but is not captured in STS
- Institutional variation — Your outcome depends not just on your risk profile but on the surgical team's experience and volume
This is precisely why a second opinion matters. A risk score is a tool, not a decision. The physicians at WhiteGloveMD combine your STS score with imaging review, clinical context, and decades of surgical experience to give you a complete picture.
Take the Next Step
Understanding your STS risk score is the first step toward making a confident decision about your cardiac care. Use our STS Risk Calculator to estimate your score, then request a second opinion from our Heart Team. WhiteGloveMD delivers AI-enhanced, dual-physician cardiac second opinions within 48 hours — because when it comes to your heart, you deserve clarity. View our pricing to get started.