Home » Patients » Multiple Sleep Latency Test
September 2020 |  Reviewed by:  Virginia Skiba, MD and Imran Shaikh, MD

What is the Multiple Sleep Latency Test?

The Multiple Sleep Latency Test (MSLT) checks for excessive daytime sleepiness by measuring how quickly you fall asleep in a quiet environment during the day. Also known as a daytime nap study, the MSLT is used to diagnose narcolepsy and idiopathic hypersomnia.

The MSLT is a full-day test that consists of five scheduled naps. After the first nap trial, each nap trial should begin 2 hours after the start of the prior nap trial. This test is always done following a sleep study that measures your sleep quality and duration. During each nap trial, you will lie quietly in bed and try to go to sleep. Once the lights go off, the test will measure how long it takes for you to fall asleep. You will be awakened 15 minutes after you fall asleep. If you do not fall asleep within 20 minutes, the nap trial will end.

Each nap will be taken in a dark and quiet sleep environment that is intended for your comfort and to isolate any external factors that may affect your ability to fall asleep. A series of sensors will measure whether you are asleep. The sensors also determine your sleep stage.

Excessive daytime sleepiness occurs when you are sleepy when you should be awake and alert. A sleep doctor will recommend an MSLT if she suspects you have excessive daytime sleepiness related to narcolepsy or a hypersomnia. The MSLT is offered at AASM-Accredited Sleep Centers. In order to provide the highest level of care for patients, the AASM requires a board-certified sleep medicine physician to review the results of the MSLT.

How to prepare for the Multiple Sleep Latency Test?

A variety of factors can affect the results of your MSLT. These include:

  • Anxiety
  • Tension
  • Depression
  • Age
  • Caffeine
  • Drugs and medications
  • Amount of sleep prior to the study

For this reason, your sleep doctor may recommend the following before your test:

  1. Keep a sleep diary for two weeks and attempt to maintain a regular sleep schedule. This will allow the doctor to see your sleep patterns. This may help identify other factors that could be causing daytime sleepiness. It will also help to ensure that you are allowing an adequate amount of time for sleep.
  2. Discuss the use of stimulants including caffeine with your sleep doctor prior to your MSLT. If you are on any medications, your doctor will help you to determine when you can use your medications before the MSLT. These substances can alter the results of your test and some medications may need to be discontinued for a couple weeks before the MSLT.
  3. The night before your MSLT you will have a sleep study. For the MSLT to be accurate, you will need to sleep at least six hours during the sleep study. A sleep study will be used to determine if another sleep disorder such as sleep apnea is causing your excessive daytime sleepiness.
  4. You may be required to take a drug test the morning of the MSLT. The drug test is to ensure that the MSLT will be accurate. There are several drugs that can affect the results. The results of the drug test will be kept private between you and your doctor.

Once you have finished these steps, you will be ready for the MSLT.

What is the testing process for the Multiple Sleep Latency Test?

The MSLT will last most of the day. Over the course of the day, you will take five scheduled naps. After the first nap trial, each nap trial should begin 2 hours after the start of the prior nap trial. Depending on the results, a shorter four-nap study may also be used. Be prepared to stay for the full five-nap version of the study.

A sleep technologist will gently place sensors on your head, face and chin. These sensors are connected to a computer. Each is long enough so you can move around and turn over in bed. The sensors show when you are asleep and awake, and transmit data used to determine when you are in REM sleep. Once you are connected, the technologist will test the sensors by asking you to move your eyes, clench your teeth and turn your head. A low-light video camera will allow the technologist to observe your MSLT from a nearby room.

The nap trial begins when the lights are turned off. You will lie quietly in bed and try to go to sleep. The MSLT will measure how long it takes you to fall asleep. It will also measure how long it takes for you to reach REM sleep.

The technologist will awaken you 15 minutes after you fall asleep. If you are unable to fall asleep, the nap trial will end after 20 minutes. At this time, you will have a break until the next nap trial begins. You will need to stay awake, and you are free to keep busy however you choose. You will start a nap trial every 2 hours.

This process will repeat four more times. After your final nap trial, you will test the sensors again and they will be removed. You are free to leave when the final trial is complete.

How are Multiple Sleep Latency Test results scored?

It will take about two weeks to get the results of your MSLT. During this time, members of the sleep team will examine the results of your MSLT.

A sleep technologist will review the data, note when you fell asleep during each nap, and look at your sleep stages and determine whether you entered REM sleep. Patients with narcolepsy often have two or more REM sleep stages during an MSLT. People with idiopathic hypersomnia fall asleep easily but do not reach REM sleep during the nap trial. Other patients may fall asleep easily, such as those with sleep apnea and insufficient sleep.

The sleep technologist will submit the results to the board-certified sleep medicine physician to interpret. The doctor will use this information to make her diagnosis.

The doctor will contact you to discuss a treatment plan. If your primary care physician or another doctor ordered the MSLT, the board-certified sleep medicine physician will send them the results.