# Multiple Sleep Latency Test (MSLT) for Narcolepsy

The MSLT is a daytime nap study done the morning after an overnight sleep study; a mean sleep latency of 8 minutes or less with two or more REM-onset naps supports a diagnosis of narcolepsy.

Updated 2026-10-28. Also on the [web page](https://sleepstudies.fyi/guides/multiple-sleep-latency-test-mslt-narcolepsy).

The **multiple sleep latency test (MSLT)** is the standard objective test for narcolepsy and idiopathic hypersomnia. It measures how quickly you fall asleep during the day and whether you enter REM sleep unusually fast.

## How the test works

1. **Night before:** an overnight polysomnography rules out other causes of sleepiness, such as sleep apnea, and confirms you slept enough.
2. **Next day:** you take **five nap opportunities at two-hour intervals**. Each starts with lights out in a quiet, dark room.
3. Each nap ends 20 minutes after lights out if you don't fall asleep, or 15 minutes after you do.
4. Between naps you stay out of bed and awake.

The full day usually ends in the late afternoon. It is billed as CPT 95805.

## What the results mean

| Finding | Interpretation |
|---|---|
| Mean sleep latency ≤8 min | Pathological sleepiness |
| 2+ sleep-onset REM periods (SOREMPs) | Supports narcolepsy |
| ≤8 min with fewer than 2 SOREMPs | May suggest idiopathic hypersomnia |

A SOREMP on the preceding night's study can count toward the total.

## Preparing

- Keep a sleep diary or wear an actigraphy watch for one to two weeks.
- Discuss medication tapering with your prescriber.
- Avoid caffeine on test day unless told otherwise.
- A urine drug screen is often done to exclude medication effects.
- Bring snacks, a book and comfortable clothes.

## Getting support

Narcolepsy Network, Project Sleep and the Hypersomnia Foundation offer patient education, and the AASM's Sleep Education site can help you find an accredited center.

## Questions

### Do I have to stop my medications before an MSLT?

Often yes. Stimulants and REM-suppressing antidepressants can distort results, so many physicians taper them about two weeks before. Only stop medications under your prescriber's direction.

### What is the difference between MSLT and MWT?

The MSLT measures how quickly you fall asleep when trying to. The maintenance of wakefulness test (MWT) measures how well you stay awake when trying not to sleep, and is used to check treatment response, including for some safety-sensitive jobs.

### Can I drive home after an MSLT?

Many centers recommend arranging a ride because the test is done for excessive sleepiness. Ask your sleep center about its policy.