Testing Nerve Conduction Velocity

Nerve conduction velocity (NCV), also called a nerve conduction study, is a noninvasive test that measures nerve function. This test involves small electrical shocks. It can be slightly uncomfortable but not painful—and it is safe.

An NCV is sometimes part of the evaluation of sensory problems, pain, and weakness of the extremities. It’s often done with an electromyography (EMG), a nerve test that involves the placement of tiny needles into the muscles. 

This article describes what you can do to prepare for NCV, what to expect, and why you might have this test.  

Nerve Conduction Velocity Test Uses

Generally, NCV is ordered to assess diseases of the peripheral nerves—those that connect from the muscles, organs, and skin to the spinal cord or brain. This test can be used to identify the type and location of nerve damage. 

Often, peripheral nerve conditions cause pain, sensory loss, tingling, or burning. Sometimes, mild weakness and diminished reflexes are detected during a neurological examination. 

Some of the conditions that are often evaluated with NCV are:

• Peripheral neuropathy: This nerve damage begins in the most distal nerves, those farthest from the center of the body, such as the toes and fingers. It is often due to chronic alcohol misuse, uncontrolled diabetes, nutritional deficits, and inflammatory diseases.
• Guillain- Barré syndrome (GBS): This inflammatory condition that causes demyelination (loss of the insulating covering around nerves) results in leg weakness. It begins in the motor nerves sending signals to muscles in the legs. The inflammation travels to nerves of the upper body, often affecting the muscles that control breathing. Respiratory support is necessary until the condition improves.
• Chronic demyelinating polyneuropathy (CIDP): This condition is a chronic, recurrent form of GBS that usually affects the legs and causes episodes of weakness.
• Radiculopathy: Often described as a pinched nerve, radiculopathy can affect an arm or a leg, causing pain and weakness.
• Myasthenia gravis (MG): This autoimmune condition affects the junction between the nerves and the muscles. Myasthenia gravis causes droopy eyelids and weakness of the arms and shoulders.
• Nerve compression: Many different conditions, including trauma, inflammation, and tumors, can cause compression of one or more nerves.
• Carpal tunnel syndrome: Commonly caused by inflammatory diseases or from overuse of the wrists, such as from assembly line work, carpal tunnel syndrome causes numbness, pain, and weakness of the fingers and hands.
• Ulnar neuropathy: This common condition causes arm pain and sensory changes, usually due to repetitive movements or a prolonged position that causes pressure on the ulnar nerve.
• ICU neuropathy: Metabolic changes, severe illness, and immobility (not moving enough) can cause nerves to develop a pattern of weakness and sensory loss.
• Amyotrophic lateral sclerosis (ALS): ALS is a serious, degenerative disease that affects the motor neurons in the spinal cord, amyotrophic lateral sclerosis progresses rapidly, resulting in substantial weakness of muscles throughout the body.

The NCV results by themselves do not diagnose a specific nerve disorder, but they can indicate nerve damage. The NCV results, along with a medical history, physical examination, and other tests, often reveal a pattern that is consistent with a specific diagnosis.

NCV testing does not help in the diagnosis of conditions that affect the brain, such as a stroke (blockage of a blood vessel or bleeding in the brain), meningitis (inflammation of the brain lining), a brain tumor, or Parkinson’s disease (progressive degeneration of the brain cells that produce the chemical messenger dopamine). 

What to Expect

If your healthcare provider orders an NCV for you, it typically requires another appointment. This test usually is done in a clinic. Sometimes, NCV testing is performed in a hospital for evaluation of certain conditions, like GBS, which may require hospitalization. 

You will not need to make any changes to your diet before having an NCV. You will be asked to avoid lotions or creams on your skin before the test.

If you are also having an EMG at the time of your NCV, you might be asked to stop taking medications or supplements that increase the risk of bleeding and bruising. If your healthcare provider says you can’t stop taking these medications for health reasons, you might be warned that you could have some bruising after the EMG test.

While it isn’t always possible, it can be helpful to wear clothes that provide access to the nerves that need to be tested in some situations. For example, if your test is to evaluate ulnar neuropathy, you can wear a shirt that can be rolled up to expose your arms.  

Preparation

When you arrive for your test, you will be asked to sign a consent form, provide your order form, and show your identification and health insurance information. You might also have to pay a co-pay (a set amount paid for each healthcare service). 

You will be led to the examination room where you will have your test, and you might be asked to take off your shoes and socks or change into a gown—this depends on which nerves you will have tested. 

You may have your temperature, pulse, and blood pressure checked prior to your test. 

During the Test

A physician typically will perform your NCV, and you might also have a technician present during your test. They might review your medical record and talk to you about your symptoms. They may also examine your muscle strength or sensation before your NCV. This would help your physician decide which nerves to test during your NCV. 

You may be asked to lie down, and your skin will be cleaned, typically with an alcohol pad, on the areas where the electrodes will be placed. 

For each nerve tested, you will have a small device, about the size of a toothbrush head, placed on your skin and another similar device placed on a different area of your skin.

You will be told when to expect a small shock sensation from the device. The sensation should go away within a few seconds. If more than one nerve is being tested, the process will be repeated for each nerve tested.

If you are having an EMG, this will be done after the NCV.

After the Test

After your test, you will be able to change or put your shoes back on. You can let the healthcare professional conducting the test know if you are feeling any discomfort or if you have any bleeding from the EMG needle (which is very rare). You should be able to leave to go home as soon as you are dressed.

Nerve Conduction Velocity Test Results

Your results will be ready in a report form about a week after the test.

An NCV test measures velocity (how fast a nerve transmits signals) and amplitude (how many nerve fibers were activated). These measurements are transmitted to a computer and shown as waves, as well as numerical values.

The values are compared to a standard measurement based on the nerve that’s being tested, the distance between the electrodes, and the person’s age. By comparison to the standard, the NCV results can identify certain patterns of nerve damage.

Outcomes of the NCV include:

• Whether one or more nerves are affected
• Whether motor nerves (those that control movement), sensory nerves (those that transmit sensory signals), or both are affected 
• Whether a nerve is blocked or damaged
• The severity of nerve damage
• The type of nerve damage, whether axonal (damage to the nerve itself) or demyelination (damage to the protective fat layer around the nerve)

These results can help point to certain diagnoses. For example, GBS causes demyelination of multiple nerves, while carpal tunnel syndrome is caused by pressure on a nerve that inhibits transmission of nerve signals.

Summary

A nerve conduction study (NCV) is a noninvasive test that measures the speed and strength of nerve stimulation, with the use of electrical probes placed on the skin. It is often part of the diagnostic process for evaluating nerve diseases.

Often, an electromyography (EMG), which is a needle test, is done at the same appointment. The results of NCV testing can be used to determine the type, severity, and location of nerve damage.

A Word From Verywell

After getting the results of your NCV study, you might need a combination of physical therapy, medical treatment, or a surgical procedure for the treatment of your condition. Most of the time, with treatment, painful symptoms of nerve diseases can improve. Treatment can often help stop the progression of conditions that cause nerve damage.