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Multiple Sleep Latency Test

What is an MSLT?

The Multiple Sleep Latency Test (MSLT) is a daytime test, used to measure how quickly you fall asleep during the day.

It is a useful test to evaluate excessive daytime sleepiness (EDS) due to any cause –hypersomnia, Narcolepsy, Sleep apnea.

What Happens During the Test?
  • The test usually starts in the morning, right after you’ve had an overnight sleep study (called a polysomnography, done the night before).
  • You will be asked to take 4–5 naps, each lasting about 20 minutes, spaced 2 hours apart.
  • During each nap, the team checks how quickly you fall asleep and what stage of sleep you enter.

    • Pre-Test Requirements of the test

    1. The Multiple Sleep Latency Test (MSLT) cannot be conducted on its own, as it requires a night prior Level 1 Polysomnography (PSG) study

    2. Sleep Schedule Monitoring (2 Weeks before Test): Adequate Sleep / Good duration of sleep or regularity of timing

    3. Medication Review and Discontinuation: Stimulants, antidepressants, sedatives, or any meds affecting sleep/wake cycles may need to be stopped 1–2 weeks prior, under medical supervision

    4. No Caffeine, Alcohol, or Nicotine: Avoid caffeine and other stimulants at least 24 hours before and during the test

    5. No Naps the Day Before: To ensure normal sleep drive at night before the test

    General Medication Guidelines before MSLT:


    Medications often allowed (under supervision):

    These medications usually do not affect sleep latency much, but always confirm with your sleep specialist:

  • Essential medications for chronic conditions (e.g., blood pressure meds, insulin, thyroid hormones)
  • Antidepressants, if you’ve been on them long-term (though some doctors might still ask for temporary discontinuation)  Medications for epilepsy (if stopping them could be risky)

    • Medications Commonly Not Allowed:

    These can alter sleep architecture, REM onset:

  • Stimulants (e.g., modafinil, amphetamines, methylphenidate) – typically discontinued 1–2 weeks before
  • Sedatives/hypnotics (e.g., benzodiazepines, zolpidem) – usually stopped several days before
  • Antidepressants(especially SSRIs, SNRIs, tricyclics) – many affect REM sleep and are often paused 2 weeks prior if clinically safe
  • Caffeine and alcohol – usually not allowed 24 hours before the test.

    • Normal MSLT Results:

  • Mean Sleep Latency (average time to fall asleep): More than 10 minutes
  • SOREMPs (Sleep-Onset REM Periods): 0 or 1 SOREMP

    • What is "abnormal" in MSLT?

    An abnormal Multiple Sleep Latency Test (MSLT) typically indicates that a person is falling asleep too quickly during scheduled nap opportunities

    Finding Possible Interpretation
    Short sleep latency (< 8 min)    Excessive daytime sleepiness (EDS), narcolepsy, idiopathic hypersomnia
    SOREMPs (2 or more)    Suggests narcolepsy
    Long sleep latency (> 10-15 min)      May indicate normal sleepiness, insomnia, or poor sleep the night before
    REM During the nap