Nerve conduction velocity test: An electrical test used to detect nerve conditions. In the nerve conduction velocity (NCV) test, the nerve is electrically stimulated by one electrode while other electrodes detect the electrical impulse "down stream" from the first electrode. The NCV test is usually done with surface patch electrodes similar to those used for an EKG (electrocardiogram). The patch electrodes are placed on the skin over the nerve at various locations. One electrode stimulates the nerve with a very mild electrical impulse. The resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission (the nerve conduction velocity, or NCV).
A decreased speed of nerve conduction indicates nerve disease. The NCV test is often done at the same time as an electromyogram (EMG) in order to exclude or detect both nerve and muscle conditions. The interpretation of an abnormal NCV test depends on why the test was done in the first place. It may indicate damage to a nerve from trauma, polio, diabetic neuropathy (nerve damage), a herniated disc, myasthenia gravis, Guillain-Barre syndrome, polyneuropathy (the simultaneous malfunction of many nerves). and many other conditions.
The patient having a NCV test lies on an examination table. The electrodes are placed on the skin over the nerve to be studied. An electrical stimulator is then placed on the skin near the electrodes and is used to create an electrical current strong enough to fully stimulate the nerve. A computer is used to record responses as various nerves are tested. The NCV test is also called a nerve conduction study, or NCS.