Article · 2 min read
MSLT and MWT Sleep Tests Explained
The MSLT and MWT are daytime sleep tests. They help diagnose narcolepsy and check how alert you are. Learn what to expect during each test.
General information, not medical advice. Read our disclaimer.
SLEEP TESTING · DAYTIME TESTS
Daytime sleep tests at a glance
- 4–5Naps in an MSLT
- 20minLength of each nap
- 40minEach of four MWT tries
- 8minAverage sleep time pointing to narcolepsy
- Both tests are done during the day.
- The MSLT measures how fast you fall asleep.
- The MSLT is the main test for narcolepsy.
- The MWT measures how well you stay awake.
- Getting ready the right way is key to accurate results.
The MSLT and MWT are sleep tests done during the day, after an overnight study. The MSLT helps diagnose narcolepsy. The MWT checks how well you can stay awake and alert.
Why are daytime sleep tests done?
The MSLT and MWT measure how sleepy or alert you are. They give doctors facts that an overnight sleep study cannot.
What is the MSLT?
MSLT stands for Multiple Sleep Latency Test. It is the main test for diagnosing narcolepsy.
- Planned naps — It measures how fast you fall asleep during 4 to 5 planned naps.
- Nap timing — Each nap is 20 minutes, with 2 hours between naps.
- SOREMPs — It looks for sleep-onset REM periods. This means you go into REM, or dreaming, sleep soon after you fall asleep.
- Signs of narcolepsy — Two results together point to narcolepsy: you fall asleep in under 8 minutes on average, and you have 2 or more SOREMPs.
What is the MWT?
MWT stands for Maintenance of Wakefulness Test. It checks how alert you are.
- Staying awake — It measures how well you can stay awake in a quiet setting.
- The test — You have four 40-minute tries in a room with dim light.
- Fitness for tasks — It is used to check if you are fit to do tasks like driving or running machines.
- Safety jobs — It is important for commercial drivers and other jobs where safety matters.
How do you get ready?
Getting ready the right way is key to accurate results.
- Overnight study first — You have an overnight sleep study (PSG, or polysomnography) the night before the MSLT.
- Regular sleep — Keep a regular sleep schedule for 1 to 2 weeks before testing.
- Medicines — You may need to stop some medicines.
SLEEP TESTING · DAYTIME TESTS
MSLT vs. MWT
| MSLT | MWT | |
|---|---|---|
| Full name | Multiple Sleep Latency Test | Maintenance of Wakefulness Test |
| What it measuresDeciding factor | How fast you fall asleep | How well you stay awake |
| How it's done | 4–5 naps, 20 minutes each, 2 hours apart | Four 40-minute tries in a dim room |
| Main use | Diagnosing narcolepsy | Checking fitness to drive or run machines |
| Key result | Under 8 minutes plus 2 or more SOREMPs | How well you stay awake |
SOREMP means going into REM (dreaming) sleep soon after falling asleep.
SLEEP TESTING · MSLT
Getting ready for an MSLT
- 1
Keep a steady schedule
Keep regular sleep times for 1 to 2 weeks first.
- 2
Review your medicines
You may need to stop some medicines before testing.
- 3
Overnight study first
You have an overnight sleep study the night before.
Key point - 4
Daytime naps
You take 4 to 5 naps, 2 hours apart.
Common questions
What is the MSLT?
Trusted medical sources
This page follows guidance and research from leading medical organizations.
Further reading
- NIHNarcolepsy
- AASMNarcolepsy
- NHLBISleep Studies
- AASMWhat to Expect at a Sleep Center
- Mayo ClinicPolysomnography
Part of our sleep studies and narcolepsy and hypersomnia services.