The NIHSS evaluates 13 areas of neurological function: level of consciousness, orientation, response to commands, gaze, visual fields, facial movement, arm motor function, leg motor function, ability to coordinate voluntary muscular movement of the limbs, response to sensory stimulation, use of language, difficulty articulating words, and inattention to stimulus on one side of the body. The patient is given a numerical score for performance in each category.
The test can be administered in five to eight minutes, and may be performed by a doctor, nurse, or therapist. The NIHSS was designed to be administered at baseline (prior to treatment), and then again two hours, 24 hours, seven to 10 days, and three months after treatment, although hospitals vary in the timing and frequency with which they administer the test.
In addition to assessing stroke severity, the NIHSS score can help guide treatment. For example, patients whose strokes are classified as mild to moderate based on their NIHSS scores are more likely to respond favorably to clot-busting drugs (thrombolytic therapy). The NIHSS score may also predict both short- and long-term stroke recovery. In one study, a baseline NIHSS score of 6 or lower strongly predicted the likelihood of a good recovery, while a score of 16 or more forecasted a high probability of severe disability or death.