Compound Muscle Action Potential Amplitude, Muscle
This test measures the size of the electrical signal produced by a muscle when its nerve is stimulated. It is part of nerve conduction studies used to assess how well nerves and muscles are communicating.
["CMAP amplitude reflects how many muscle fibers respond to a nerve signal, helping evaluate nerve and muscle function."]
Key facts at a glance
- LOINC
- 98713-1
- Short code
- CMAP amplitude Muscle
- Synonyms
- CMAP amplitude Muscle
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- nerve-conduction
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What This Test Measures
The compound muscle action potential (CMAP) amplitude is the height of the electrical response recorded from a muscle after its supplying nerve is electrically stimulated. A larger amplitude generally means more muscle fibers are responding to the nerve signal.
How the Test Is Done
Small surface electrodes are placed over the muscle, and a brief electrical pulse stimulates the nerve. The recording device captures the resulting waveform and its amplitude. The procedure is quick, and discomfort is usually mild and brief.
Why It May Be Ordered
Doctors order CMAP amplitude as part of nerve conduction studies to investigate weakness, numbness, tingling, or muscle wasting. It helps distinguish problems with the nerve, the neuromuscular junction, or the muscle itself.
What Results Can Mean
Reduced amplitude may suggest loss of nerve fibers or muscle fibers, while normal or increased amplitude can occur in certain conditions. Results are interpreted alongside other nerve conduction and clinical findings, and specific reference values vary by laboratory and muscle tested.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
CMAP amplitude is a key measurement in electrodiagnostic testing. Low values can point to axonal nerve damage or myopathy, whereas normal values with other abnormalities may suggest demyelination. Interpretation requires correlation with the patient's symptoms, physical exam, and other nerve conduction results.
Short name
CMAP Amplitude
Frequently asked questions
Does the test hurt?
Do I need to prepare for the test?
Can I take my medications before the test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy