The Multiple Sleep Latency Test

Multiple Sleep Latency Test

Do you feel drowsy most of the time? Do you doze off when you’re supposed to be awake? If you said yes to either question, you might have excessive daytime sleepiness. To accurately identify the cause, medical professionals may conduct a multiple sleep latency test (MLST).

Getting enough hours of shut-eye at night is vital for your health and wellness. But too much of it may signal a problem. MLST is one of the initial steps that can help if you’re falling asleep more often than you should.

MLST focuses on diagnosing narcolepsy and hypersomnia, for which symptoms include excessive sleepiness. These sleep disorders are worth paying attention to as they can affect your daily activities. They can hinder your performance at work, in school, or at home. In this light, we’ll also dish out tips on how to deal with them.

Excessive Daytime Sleepiness

Excessive sleepiness is not a disorder but a symptom. Narcolepsy and idiopathic hypersomnia are two possible causes. Both are neurological disorders that affect your sleep-wake cycle. If you suspect you have one of these conditions, you may rule out other causes through an MLST. 


On top of excessive sleepiness and tiredness, narcolepsy is characterized by instantly dozing off regardless of your activity. People with narcolepsy drift into the REM (Rapid Eye Movement) phase of sleep during the sleep cycle and even when awake. This disorder shares similar qualities, such as sleep paralysis and vivid dreams, with the body’s state during the REM stage.

There are two types of narcolepsy:

  • Type 1 – Strong emotions trigger attacks. For symptoms, excessive sleepiness always combines with deficient or absent CSF hypocretin-1 levels. Type 1 narcolepsy may also include cataplexy, which involves the loss of muscle tone. It can sometimes lead to slurred speech, buckling knees and paralysis at some point.
  • Type 2 – Narcolepsy without cataplexy is considered type 2. 

Idiopathic Hypersomnia

Excessive sleepiness during the day also characterizes idiopathic hypersomnia. It can happen even after you had a full night’s sleep earlier. Other symptoms include being hard to wake up after falling asleep. It does not matter whether it’s from an evening slumber or a nap.

The disorder is similar to narcolepsy. However, those who have it do not experience sleep attacks and cataplexy—falling asleep all of a sudden and losing muscle tone when going through intense emotions, respectively. 

Yet, it’s hard to feel refreshed even after catching some zzzs. You may still feel drowsy no matter how many hours you already slept or how many times you took a nap.

Read: 5 Sleep Disorders You Should Know Aside From Insomnia

Sleep Latency

What Happens During a Multiple Sleep Latency Test?

A multiple sleep latency test is a study that measures the time it takes for you to fall asleep during the day. It’s conducted in a controlled and quiet environment. It’s typically done right after an overnight polysomnogram (PSG). During a PSG, medical professionals record your nighttime sleep patterns. The morning after, you’ll then be asked to take naps at a two-hour interval.

Here is a breakdown of what usually happens in an MLST:

  • After the PSG, you’ll change into daytime clothing and perform a typical morning routine, which includes eating breakfast. Then, you’ll be asked to return to bed and take a nap.
  • You’ll be awakened after 15 minutes of falling asleep. If you don’t doze off within 20 minutes, though, the facilitators will end the nap. Some of the testing sensors from the PSG aren’t removed from your head and face throughout the day. They’ll be used to monitor your sleeping, waking, and REM states.
  • Other activities monitored include your heart’s and brain’s electrical activities, oxygen levels, eye movements, breathing, and extremity movements.
  • You’ll take similar naps for about 3 or 4 times more, often with a 2-hour interval.
  • In between the tests, you will be able to act out your day normally like perform chores, work or study, eat and use the bathroom. However, you won’t be allowed to exercise or do something strenuous. 

MLST will measure your sleep latency (how fast you fall asleep) during the nap trials. Indicators of narcolepsy or idiopathic hypersomnia are:

  • Narcolepsy – a mean latency below eight minutes and entering REM sleep in two naps.
  • Idiopathic hypersomnia – a mean latency below eight minutes and entering REM sleep in just one nap.

Who Should Take the Test?

So you feel the need to sleep throughout the day and want to know why. You may suspect you have narcolepsy or idiopathic hypersomnia. Your physician may consider a multiple sleep latency test to rule out other disorders.

Those ages two and up are cleared to undergo MLST. They must also consult with a board-certified sleep physician who will not only recommend the test but also prepare them for it. 

Take note that there is an array of factors that can affect your test results. These include age, amount of sleep before the study, anxiety, depression, tension, caffeine, drugs, and medications. So preparation is important.

Here are the steps you’ll need to take to prepare for an MLST.

  • Record your sleep-wake patterns for two weeks. Your doctor should provide you with instructions on how to keep a sleep diary. This will not only help them understand if other factors are causing your excessive daytime sleepiness, but will also monitor how much sleep you are getting and if you’re getting enough.
  • Chemicals and substances can affect your MLST results. So if you are drinking caffeine or taking medications, make sure to let your sleep physician know. They will determine the proper timing for having them before your MLST.
  • Prepare to take the overnight polysomnogram. The PSG also called the sleep study, requires you to sleep for a minimum of 6 hours. It will help check if a different sleep disorder is causing excessive sleepiness.
  • You may then be asked to take a drug test before you start the MLST in the morning. Again, drugs and medications can alter the results of the test. So this is a standard test to ensure the results will be accurate. For the purposes of this study, the drug test results will be kept private.

How to Deal With Sleep Disorders

Dealing with neurological disorders can be challenging. But with the help of your doctor and the people around you, proper self-care is possible.

Dealing With Narcolepsy

Take a Nap

Experts recommend taking a 15 to 20-minute nap during the time you find it most challenging to stay awake. Most people peak in the afternoon, but if you feel intense drowsiness several times a day, you may schedule a short nap in the morning, too. Drivers with narcolepsy may need a quick shut-eye before they drive.

Keep Moving

If you work or study, you probably have to sit for extended hours. To avoid falling asleep, you need to keep moving. Take a short walk outside your office or classroom.

Get Enough Sleep

Make sure you are getting a full night’s sleep. This is vital to feel refreshed. Some patients become more prone to cataplexy when they are tired.

More self-care tips can be found here.

Dealing With Idiopathic Hypersomnia

Drink Caffeine

People with idiopathic hypersomnia may not feel fully awake during the day. Drinking coffee, twice with 100 mg of caffeine dose each, may help to achieve wakefulness. Caffeine is a mild stimulant and readily available. Avoid taking it close to bedtime as it tends to affect sleep onset. 

Get Enough Sleep

Treating the symptoms of idiopathic hypersomnia is similar to treating the symptoms of narcolepsy. This is because both disorders fall under the umbrella category of hypersomnias. 

Despite the lack of refreshing effects in idiopathic hypersomnia patients, you should still aim for a full night’s sleep.

Make sure your sleep environment at night is cool and quiet. Set the air conditioning to a lower temperature. Shut the curtains and turn off the television. When your sleep is interrupted, avoid stimulating activities like checking your phone. Read a book or listen to quiet music instead.


Excessive sleepiness may be caused by narcolepsy or idiopathic hypersomnia. One of the best ways to find out if you have either is the multiple sleep latency test. To take the MLST, you will need to prepare yourself physically. Drugs and medications, as well as anxiety and depression, can alter the results of your MLST.

You’ll also need to go through the overnight sleep study the night before your MLST. Thus, you must prepare for both tests. Your board-certified sleep physician should be able to help you with this.

Spare an entire day for the sleep latency test, which will measure how fast you fall asleep. The results can help your physician tell if you have narcolepsy or idiopathic hypersomnia. And once you’re diagnosed with either disorder, it will be easier to treat the symptoms. Over time, you will also learn how to cope and conquer your disorder better.

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