Malignant Hyperthermia Clinical Grading Scale Calculator

Larach Clinical Grading Scale for malignant hyperthermia likelihood (MH rank 1–6).

For educational and clinical reference. Not a substitute for medical judgment. See the medical disclaimer.

Process I — Muscular rigidity

Process II — Muscle breakdown (highest applicable)

Process III — Respiratory acidosis (highest applicable)

Process IV — Temperature increase (highest applicable)

Process V — Cardiac involvement

Process VI — Family history of MH

Other indicators (highest applicable)

Score

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Interpretation

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References

Larach MG, Localio AR, Allen GC, et al. A clinical grading scale to predict malignant hyperthermia susceptibility. Anesthesiology. 1994;80(4):771-779.

How to use

For each clinical process, select the single highest applicable indicator.
The raw CGS score and MH likelihood rank update instantly.
Use retrospectively to grade likelihood — confirm susceptibility with formal testing.

Frequently asked questions

What is the MH Clinical Grading Scale?

The Larach Clinical Grading Scale estimates the qualitative likelihood that an event was malignant hyperthermia by summing the highest indicator within each clinical process.

How is the raw score ranked?

< 9 = rank 1 (almost never), 10–19 rank 2, 20–34 rank 3, 35–49 rank 4, 50–64 rank 5, ≥ 65 rank 6 (almost certain).

Why pick only the highest indicator per process?

The CGS scores each process once (its highest applicable indicator) to avoid double-counting correlated findings; the process scores are then summed.

Is the CGS diagnostic?

No — it grades clinical likelihood retrospectively. Definitive diagnosis uses caffeine-halothane contracture testing or genetic testing.

Last updated June 28, 2026