Maintenance of Wakefulness Test (MWT)

Updated on June 13, 2022

Medically reviewed by Smita Patel, MD

In individuals who have excessive daytime sleepiness, the maintenance of wakefulness test (MWT) may be a useful diagnostic test to identify an inability to stay awake.

Doctor writing something observing person asleep in bed — KatarzynaBialasiewicz / Getty Images

What Is the MWT?

The MWT is a test meant to objectively measure your ability to stay awake, which can infer how sleepy you are. The test may be used to assess your response to treatment of various sleep disorders, including sleep apnea or narcolepsy.

Performing the MWT

The MWT typically begins 1 1/2 to 3 hours after you usually wake up.

Prior to the test, you will complete a questionnaire, which includes questions about whether your previous night's sleep was of adequate quantity and quality, and whether you feel alert. You will then be placed in a dim room, with the only source of light slightly behind your head and out of your field of vision. You will usually be sitting upright in bed, with your back and head supported.

You will be instructed to stay awake as long as possible. During this time you will be monitored with the same measures that are used in a standard overnight sleep study called a polysomnogram.

The session will end if you fall asleep, or if you go 40 minutes without falling asleep. The sleep latency, or the time it takes you to fall asleep, will be recorded. This is repeated every two hours until four sessions have been completed.

How Is MWT Used?

In healthy people, the time it takes to fall asleep may be approximately 30 minutes on the test. More than 97% of people will take eight minutes or longer to fall asleep. Therefore, sleep latency that is less than eight minutes is considered to be abnormal. If you are able to stay awake during all four sessions, it is unlikely that you have difficulty maintaining wakefulness.

Limitations

Although MWT measures sleep latency, it is not a substitute for a related test called the MSLT, which also measures how long it takes you to fall asleep. In fact, the two tests may give different results, even in the same person on the same day. Moreover, the test takes a long time to complete and because it involves specialized monitoring, it can be expensive. Therefore, MWT may not be the best test for everyone to determine the degree of sleepiness.

Sources

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Littner, M et al. "Practice parameters for clinical use of the multiple sleep latency test and the maintenance of wakefulness test." Sleep 2005;28:113.
Mitler, MM et al. "Methods of testing for sleepiness [corrected]." Behav Med 1996;21:171.
Mitler, MM et al. "Sleep latency on the maintenance of wakefulness test (MWT) for 530 patients with narcolepsy while free of psychoactive drugs." Electroencephalogr Clin Neurophysiol 1998;107:33.