McMahon Score for Rhabdomyolysis

McMahon Calculator
Age ≥70 years
Female Sex
Initial Creatine Kinase (CK)
Initial Phosphate
Initial Calcium
Initial Creatinine
Cause of Rhabdomyolysis
McMahon Score: 0
Low Risk
0 points: Low risk of death or need for renal replacement therapy (RRT).
Predicts mortality or acute kidney injury (AKI) in rhabdomyolysis patients.

Why Use

Uses readily available clinical demographic and laboratory values. More specific than CPK alone at predicting need for RRT ( AUROC 0.775 vs 0.631).

When to Use

Patients ≥18 years old with rhabdomyolysis (CPK >5,000 U/L within 72 hours of admission). Do not use in patients with pre-existing end-stage renal disease or elevated CPK due to MI.

Formula

Addition of the selected points: Variable Points Age, years ≤50 0 51–70 1.5 71–80 2.5 >80 3 Sex Male 0 Female 1 Initial creatinine <1.4 mg/dL (124 µmol/L) 0 1.4–2.2 mg/dL (124–195 µmol/L) 1.5 >2.2 mg/dL (195 µmol/L) 3 Initial calcium <7.5 mg/dL (1.88 mmol/L) No 0 Yes 2 Initial CPK >40,000 U/L No 0 Yes 2 Rhabdo secondary to seizures, syncope, exercise, statins, or myositis Yes 0 No 3 Initial phosphate <4.0 mg/dL (1.0 mmol/L) 0 4.0–5.4 mg/dL (1.0-1.4 mmol/L) 1.5 >5.4 mg/dL (1.4 mmol/L) 3 Initial bicarbonate <19 mEq/L (19 mmol/L) No 0 Yes 2

Pearls / Pitfalls

Can be used in both traumatic and atraumatic rhabdomyolysis. Not validated for patients who have had renal replacement therapy (RRT) within 24 hours. Not yet prospectively validated (has been retrospectively validated ).

Management

Renal protective therapy should include fluid resuscitation targeting euvolemia and urinary output of at least 1–2 mL/kg/hr.

Critical Actions

Renal protective therapies should be considered in all patients deemed to be at high risk (score ≥6) irrespective of admission CPK.

Advice

CPK >1,000 U/L provides laboratory confirmation of the clinical diagnosis (CPK >40,000 U/L is used as a risk factor in the score). Delayed increase in CPK is common and therefore serial levels should be obtained.

More Information

Interpretation: McMahon Score Risk group Recommendation <6 Low risk Usual care (3% risk of death or AKI requiring RRT) ≥6* Not low risk Initiate renal protective therapy including high-volume fluid resuscitation to urine output 1-2 mL/kg/hr (52% risk of death or AKI requiring RRT at scores ≥10) From Simpson 2016 . *McMahon Score ≥6, calculated on admission, is 86% sensitive and 68% specific for identifying patients who will require RRT.

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