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.