Doctors evaluate patients for narcolepsy with sleep studies, which exist in the forms of polysomnograms and multiple sleep latency tests, as well as the hypocretin test, explains the National Heart, Lung, and Blood Institute. Sleep studies monitor sleeping behaviors, while a hypocretin test measures the hypocretin around the spinal cord.
Patients usually spend a night at a sleep center to undergo polysomnograms, notes the National Heart, Lung, and Blood Institute. Throughout the night, the polysomnogram machine records data about the patient's eye movements, blood pressure, brain activity and heart rate. The physician then uses the recorded data to check for indicators of narcolepsy, such as how quickly the patient falls asleep and whether the patient enters into rapid eye movement, or REM, shortly after going to sleep. A multiple sleep latency test is another type of sleep study that often follows a polysomnogram. This test involves taking frequent naps throughout the day to assess how quickly the patient falls asleep and subsequently enters REM sleep when well-rested.
Hypocretin is a chemical found in the fluid around the spinal cord, states the National Heart, Lung, and Blood Institute. Patients who have narcolepsy often lack sufficient levels of the chemical, which promotes wakefulness. In addition to sleep studies, a doctor can perform a spinal tap to check the level of hypocretin in a patient's spinal cord fluid when narcolespy is suspected.