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    McMahon Score for Rhabdomyolysis

    Predicts mortality or acute kidney injury (AKI) in rhabdomyolysis patients.
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    INSTRUCTIONS

    Use in 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 with elevated CPK due to MI.

    When to Use
    Pearls/Pitfalls
    Why 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.

    • 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).

    • Uses readily available clinical demographic and laboratory values.

    • More specific than CPK alone at predicting need for RRT (AUROC 0.775 vs 0.631).

    ≤50
    0
    51-70
    +1.5
    71-80
    +2.5
    >80
    +3
    Male
    0
    Female
    +1
    <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
    No
    0
    Yes
    +2
    No
    0
    Yes
    +2
    Yes
    0
    No
    +3
    <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
    No
    0
    Yes
    +2

    Result:

    Please fill out required fields.

    Next Steps
    Evidence
    Creator Insights

    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.

    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.

    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

    Facts & Figures

    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.

    Evidence Appraisal

    Derivation study, McMahon 2013.

    • Design:

      Retrospective study in two teaching hospitals, n = 2,371.

    • Aim:

      Derive and validate a risk prediction equation to estimate risk of RRT or death in patients with rhabdomyolysis.

    • Inclusion criteria:

      • Age ≥18 years.

      • CPK levels >5,000 U/L within 72 hours of admission.

    • Exclusion criteria:

      • Preexisting end-stage renal disease.

      • Patient receiving RRT for at least 24 hours.

      • CPK elevation considered due to acute MI.

    • Outcomes:

      • In-hospital mortality: 335 patients (14%).

      • AKI: 1,081 patients (46%).

      • Need for RRT: 190 patients (8%).

    Validation study, Simpson 2016.

    • Design:

      Retrospective observational, n = 232.

    • Aims:

      • Identify CPK thresholds to guide clinical management.

      • Evaluate the prognostic performance of McMahon Score.

    • Inclusion criteria:

      • Age ≥18 years.

      • CPK levels > 1,000 U/L.

    • Exclusion criteria:

      Not listed.

    • Outcomes:

      • In-hospital mortality: 86 (11%).

      • Acute renal failure: 45 patients (19%).

      • Need for RRT: 29 patients (12.5%).

    Dr. Gearoid M. McMahon

    About the Creator

    Gearoid M. McMahon, MD, MB, BCh, is a nephrologist at Brigham and Women's Hospital in Boston. He is also one of the editors of the popular nephrology resource Renal Fellow Network. Dr. McMahon’s research focuses primarily on acid-base disorders, acute renal failure, glomerular disease, and kidney stones.

    To view Dr. Gearoid M. McMahon's publications, visit PubMed

    Content Contributors
    About the Creator
    Dr. Gearoid M. McMahon
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