Mehran Score for Contrast-Induced Nephropathy Risk Assessment
What is the Mehran Score?
The Mehran score is a validated clinical risk prediction tool that stratifies patients into four risk categories (low ≤5, moderate 6-10, high 11-15, and very high ≥16) for developing contrast-induced nephropathy (CIN) after percutaneous coronary intervention, and it reliably predicts both short-term renal complications and long-term mortality. 1, 2
The score incorporates eight clinical and procedural variables to calculate total risk points 1:
- Hypotension (systolic BP <80 mmHg for at least 1 hour requiring inotropic support)
- Intra-aortic balloon pump use
- Congestive heart failure (NYHA class III/IV or history of pulmonary edema)
- Age >75 years
- Anemia (baseline hematocrit <39% for men, <36% for women)
- Diabetes mellitus
- Contrast media volume
- Baseline renal function (serum creatinine or estimated GFR)
Clinical Application and Risk Stratification
The Mehran score demonstrates robust predictive capability across multiple clinical scenarios. In primary PCI for ST-elevation myocardial infarction, patients in the very high-risk group (≥16) had more than 10-fold higher mortality (HR 10.11,95% CI 4.83-21.1) compared to low-risk patients 1. Similarly, high-risk patients showed 6-fold increased mortality (HR 6.31,95% CI 3.28-12.14) 1.
The score's predictive value extends beyond CIN to forecast major adverse cardiovascular and cerebrovascular events (MACCE), with the very high-risk group showing nearly 4-fold increased risk (HR 3.79,95% CI 2.27-6.32) and 6-fold increased mortality at 2 years (HR 6.22,95% CI 2.77-13.95). 1, 2
Risk Category Outcomes
- Low risk (≤5): CIN incidence 0.5-1.1% 2, 3
- Moderate risk (6-10): CIN incidence 3.4% 3
- High risk (11-15): CIN incidence 15.9%; this group is an independent predictor of CIN with persistent renal dysfunction (OR 3.35,95% CI 1.89-5.92) 2, 3
- Very high risk (≥16): CIN incidence 37.5%; associated with dramatically increased mortality and MACCE 2, 3
Practical Implementation in Clinical Practice
Calculate the Mehran score before any contrast-enhanced procedure in patients undergoing PCI, particularly in acute myocardial infarction, chronic total occlusion interventions, and transcatheter aortic valve implantation settings. 1, 4, 2
For high-risk (11-15) and very high-risk (≥16) patients, implement aggressive preventive strategies 5:
- Hydration with isotonic saline (1.0-1.5 mL/kg/hour) for 3-12 hours before and 6-24 hours after contrast exposure 6, 5
- Minimize contrast volume: Use <350 mL or <4 mL/kg, or maintain contrast volume/creatinine clearance ratio <3.7 6, 5
- Use low-osmolar or iso-osmolar contrast media 5
- Consider short-term high-dose statin therapy (rosuvastatin 40 mg, atorvastatin 80 mg, or simvastatin 80 mg) 5
Comparison with Alternative Risk Models
Recent evidence suggests the contrast volume-to-GFR ratio (CV/GFR) may offer comparable predictive accuracy to the Mehran score with greater simplicity. In older adults undergoing coronary angiography, the CV/GFR ratio showed similar area under the curve (0.79,95% CI 0.65-0.92) compared to the Mehran score (0.65,95% CI 0.51-0.82) 7. However, the Mehran score provides more comprehensive risk stratification by incorporating multiple clinical variables beyond renal function and contrast volume 1, 2.
Critical Caveats and Pitfalls
Do not rely solely on baseline creatinine without calculating estimated GFR, as creatinine alone underestimates renal dysfunction, particularly in elderly patients and those with reduced muscle mass. 6, 8
The Mehran score was originally validated in non-urgent PCI but has demonstrated utility in primary PCI for STEMI, chronic total occlusion interventions, and TAVI procedures 1, 4, 3. In chronic total occlusion PCI, severe vessel tortuosity independently predicts CIN (OR 6.62,95% CI 1.09-40.23) beyond the Mehran score alone 3.
Patients with Mehran scores ≥11 require post-procedure monitoring with repeat serum creatinine measurement 48-96 hours after contrast exposure to detect CIN, which typically manifests within this timeframe. 8
Approximately 46% of patients who develop CIN may experience persistent renal dysfunction rather than transient injury, particularly in high-risk groups, emphasizing the importance of aggressive prevention in patients with elevated Mehran scores 2.