What tests are used to diagnose narcolepsy?

The following tests are used to diagnose narcolepsy:

1. Sleep Study or Polysomnogram (PSG): This painless test is done at night, usually at a sleep center. While you're sleeping, electrodes measure breathing, any breathing difficulty, oxygen levels, brain waves, eye and muscle movement, and your heart rate.

If there are any abnormalities to your sleep cycle—for example, you experience REM (rapid eye movement, which occurs when you're dreaming) at abnormal times—this will help the healthcare provider rule out other causes.

2. Multiple Sleep Latency Test (MSLT): The MSLT is completed during the day. It measures how long it takes you to fall asleep. You'll take a short nap a few times during the day. If you're able to fall asleep within 8 minutes and/or you achieve REM within a couple minutes of falling asleep, you may have narcolepsy.

Together, these two tests go a long way to helping determine whether you have narcolepsy, but they don't tell the whole story. If you don't experience cataplexy (sudden muscle tone loss) too, we need to rule out other potential causes of your sleepiness.

There is a third test—but it's not for everyone. It's called a human leukocyte antigen typing. It measures hypocretin, the brain chemical that is thought to cause narcolepsy in some cases. The test involves taking a sample of cerebrospinal fluid through your lumbar spine.