Diagnosing Narcolepsy

Medically Reviewed by Sabrina Felson, MD on July 16, 2023
3 min read

A narcolepsy diagnosis requires several tests. A doctor will perform a physical exam and an in-depth medical history to rule out other causes of symptoms. Keep in mind that having some of the major symptoms of narcolepsy doesn't necessarily mean you have narcolepsy.

In addition, several specialized tests, which can be performed in a sleep disorders clinic, are usually required before a diagnosis can be established. Two tests considered essential in confirming a diagnosis of narcolepsy are the:

  • Polysomnogram (PSG)
  • Multiple sleep latency test (MSLT)

In addition, questionnaires, such as the Epworth Sleepiness Scale, are used to measure excessive daytime sleepiness.

You’ll need a sleep specialist for some of these tests.

During this test, you will be asked to answer eight questions using a scale from 0 (not at all likely to fall asleep) to 3 (very likely to fall asleep). The resulting score is between 0 and 24. Scores of 0 to 10 are normal. Total scores 10 or above generally warrant further investigation.

You take the Epworth Sleepiness Scale test at home. You don’t have to spend the night in a sleep clinic for it.

A sleep study, or polysomnogram (PSG), is a test performed in a sleep lab. It electronically transmits and records specific physical actions of the body while you sleep, such as muscle movement, breathing patterns, and brain activity. The recordings are analyzed by a qualified sleep specialist to determine whether or not you have a particular sleep disorder.

If you're scheduled for a PSG, you will arrive at the sleep lab about 2 hours prior to bedtime without making any changes in your daily habits. You'll be assigned to a private bedroom in a sleep center or hospital. Near the bedroom will be a central monitoring area, where the technicians will monitor you while you sleep.

You will be hooked up to equipment that may look uncomfortable. However, most people fall asleep with little difficulty. Your whole night's sleep will be monitored and recorded.

Here are some guidelines for the day leading up to your PSG. These will help your sleep specialist get the most accurate reading:

  • Eat and take your medications as usual.
  • Don’t take naps.
  • Wash and dry your hair.
  • Take off nail polish or acrylic nails if you’re wearing them.

And don’t forget to bring these things with you:

  • Any medications you’ll need to take while you’re there
  • Pajamas
  • Toiletries
  • Things that might help you sleep better, like your favorite pillow

Performed the morning after the overnight polysomnogram, also in a sleep lab, this test measures how long it takes a person to fall asleep (sleep latency) during the day. During this test, you will be asked to take four or five scheduled naps every 2 hours. The first nap starts 2 hours after awakening that morning.

People with normal sleep and alertness take about 10-20 minutes to fall asleep. People with narcolepsy (and other causes of abnormal sleepiness) take a much shorter time (less than 5 minutes) to fall asleep.

Two weeks prior to these tests, you will be asked to keep a sleep diary to keep track of:

  • Bedtimes
  • Wakeup times
  • Nap times

Your doctor will work with you to create a plan to gradually eliminate medications that could affect the sleep test results.

If your doctor tells you that you have narcolepsy, they may do something called a lumbar puncture. They’ll take some fluid from your spine to find out if you have enough of a brain chemical called hypocretin. It helps you sleep and wake up at the right times.

Your doctor also might run a blood test or brain scan to make sure that you really have narcolepsy and not a different condition.

You might need a few more sleep tests once your daytime sleepiness is under control.