How is the Mehran score used to assess risk of contrast-induced nephropathy (CIN)?

How the Mehran Score is Used to Assess Risk of Contrast-Induced Nephropathy

The Mehran score is a validated risk stratification tool that assigns points based on eight clinical variables to predict both the probability of developing contrast-induced nephropathy and the need for dialysis following contrast exposure, with scores categorized into four risk groups that guide preventive strategies.

Components of the Mehran Score

The Mehran score incorporates the following risk factors with their respective point values 1:

• Hypotension (5 points) 1
• Intra-aortic balloon pump use (5 points) 1
• Chronic heart failure (5 points) 1
• Age >75 years (4 points) 1
• Anemia (3 points) 1
• Diabetes mellitus (3 points) 1
• Contrast volume (1 point per 100 mL) 1
• Renal function impairment: 1
  • Serum creatinine >1.5 mg/dL (4 points), OR
  • eGFR-based scoring: 2 points for eGFR 40-60 mL/min, 4 points for eGFR 20-40 mL/min, 6 points for eGFR <20 mL/min

Risk Stratification and Predicted Outcomes

The total score stratifies patients into four distinct risk categories with corresponding probabilities 1:

• Low risk (score <5): 7.5% risk of CIN, 0.04% risk of dialysis 1
• Moderate risk (score 6-10): 14% risk of CIN, 0.12% risk of dialysis 1
• High risk (score 11-16): 26.1% risk of CIN, 1.09% risk of dialysis 1
• Very high risk (score >16): 57.3% risk of CIN, 21.6% risk of dialysis 1

Clinical Validation and Prognostic Value

The Mehran score has been extensively validated across multiple populations and predicts not only CIN development but also short- and long-term mortality and major adverse cardiovascular events. 2, 3

• In ST-elevation myocardial infarction patients undergoing primary PCI, the very high-risk group demonstrated more than 10-fold higher mortality (HR 10.11,95% CI 4.83-21.1) compared to the low-risk group 2
• The score maintains excellent discriminatory capacity with C-statistic values >0.8 in contemporary acute coronary syndrome populations 3
• Higher risk scores independently predict persistent renal dysfunction following CIN, not just transient creatinine elevation 4

Practical Application in Clinical Decision-Making

Calculate the Mehran score before any contrast procedure in patients with identifiable risk factors to determine the intensity of preventive measures required. 1, 5

For Low-Risk Patients (Score <5):

• Standard isotonic saline hydration (1.0-1.5 mL/kg/hour) for 3-12 hours before and 6-24 hours after contrast 5
• Use low-osmolar or iso-osmolar contrast media 5
• Minimize contrast volume to <350 mL or <4 mL/kg 5

For Moderate-Risk Patients (Score 6-10):

• Aggressive intravenous hydration with isotonic saline as above 5
• Consider sodium bicarbonate hydration as alternative (154 mEq/L at 3 mL/kg for 1 hour before, then 1 mL/kg/hour for 6 hours after) 5
• Short-term high-dose statin therapy (rosuvastatin 40 mg, atorvastatin 80 mg, or simvastatin 80 mg) 5
• Strict contrast volume minimization 5

For High and Very High-Risk Patients (Score ≥11):

• Mandatory aggressive hydration protocols 5
• High-dose statin therapy 5
• Minimize contrast volume to absolute minimum necessary 5
• For stage 4-5 CKD with very high scores, consider prophylactic hemofiltration before complex interventions 5
• Post-procedure creatinine monitoring at 48-96 hours 6

Important Caveats and Limitations

While the Mehran score demonstrates excellent overall performance, its sensitivity may be reduced specifically in primary PCI populations where baseline renal function is often unknown at the time of urgent contrast exposure. 7

• The score was originally derived from non-urgent PCI populations, and some studies show lower discriminatory capacity (AUC 0.59) in acute MI settings 7
• Despite this limitation, the score remains clinically useful as higher scores consistently correlate with worse outcomes even in emergency situations 2, 4
• Do not use the Mehran score as justification to withhold necessary contrast procedures in high-risk patients—instead, use it to intensify preventive measures and inform post-procedure monitoring 1, 5

What NOT to Do Based on Mehran Score Results

• Do not administer N-acetylcysteine as a substitute for proper hydration, regardless of risk score, as it provides no benefit 5
• Do not perform prophylactic hemodialysis in stage 3 CKD patients even with elevated scores 5
• Do not rely on creatinine alone without calculating eGFR when determining the renal function component of the score, as this underestimates dysfunction particularly in elderly patients 5, 6