McMahon Score: A Prognostic Tool for Rhabdomyolysis-Related Acute Kidney Injury and Mortality
The McMahon score is a validated prognostic model that predicts acute kidney injury (AKI) risk and in-hospital mortality in patients with rhabdomyolysis, with a score ≥6 indicating significantly increased risk of adverse outcomes.
What the McMahon Score Measures
The McMahon score is calculated using readily available clinical and laboratory variables at hospital admission. While the specific variables aren't detailed in the provided evidence, the score stratifies patients into risk categories for:
- Acute kidney injury development
- Need for renal replacement therapy (dialysis)
- In-hospital mortality
Clinical Performance and Validation
The score demonstrates robust predictive accuracy across multiple rhabdomyolysis etiologies:
Mortality Prediction
- Area under the curve (AUC): 0.936-0.951 across different studies 1, 2
- A cut-off score ≥6 yields 71.4-83.3% sensitivity and 89.2-100% specificity for mortality prediction 1, 2
- Mortality probability exceeds 90% when the score reaches ≥10 1
AKI Prediction
- AUC of 0.807 for predicting AKI development 3
- Score >6 optimally predicts AKI with superior performance compared to creatine kinase (CK) levels alone 3
- Strong positive correlation (r = 0.998) between McMahon score and AKI risk percentage 1
Hemodialysis Requirement
- The McMahon score is superior to CK levels in predicting the need for renal replacement therapy 3
Clinical Applications by Etiology
The score has been validated in multiple rhabdomyolysis contexts:
Electrocution-induced rhabdomyolysis:
- In-hospital mortality 3.5%; patients who died had mean scores of 7.4 vs. 3.4 in survivors 1
Poisoning-induced rhabdomyolysis:
- AKI rate 34%, mortality 6%; McMahon score ≥6 independently associated with AKI development 3
Lightning strike-induced rhabdomyolysis:
- Mortality rate 21.2%, AKI incidence 7.0%; scores >6 associated with significantly higher adverse outcomes 2
Risk Stratification Algorithm
Score <6: Low risk
- Favorable prognosis expected
- Standard supportive care appropriate
Score ≥6: High risk
- Significantly increased AKI and mortality risk
- Requires aggressive fluid resuscitation, close monitoring
- Early nephrology consultation warranted
- Consider ICU-level care
Score ≥10: Very high risk
- Mortality probability >90%
- Immediate intensive care required
- Prepare for likely need for renal replacement therapy
Clinical Advantages
The McMahon score offers several practical benefits:
- Simplicity: Uses readily available admission data without requiring specialized testing
- Speed: Enables rapid risk assessment in emergency settings
- Accuracy: Outperforms isolated biomarkers like CK for predicting clinically meaningful outcomes
- Versatility: Validated across diverse rhabdomyolysis etiologies (trauma, electrical injury, poisoning, lightning strikes)
Important Caveats
Independent risk factors for AKI in rhabdomyolysis patients include age >33 years, McMahon score ≥6, and WBC count >18 × 10³/µL 3. The score should be interpreted alongside these clinical parameters rather than in isolation.
The score's primary utility is early risk stratification at admission to guide intensity of monitoring and intervention, not as a dynamic tool for ongoing assessment.
Note: The McMahon score is distinct from contrast-associated AKI risk scores used in percutaneous coronary intervention 4. Do not confuse these separate clinical tools.