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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 separated by two-hour breaks. 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 after sleeping 15 minutes. 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.