Respiratory Question for the Week of October 30, 2023


Can you explain the details behind the service of MSLT? We want a clearer understanding in order to know what codes we should report.


Sometimes referred to as nap testing, MSLT is performed as a series of recordings to monitor the patient’s sleep patterns in order to evaluate excessive daytime sleepiness and narcolepsy (sudden and uncontrollable onsets of sleep). This test measures how long it takes to fall asleep during the course of a day. A video camera records movements during sleep. Eye movements, brain electrical activity, and muscle-tone changes are recorded during 15- to 20-minute naps, spaced about 2 hours apart. The procedure typically starts at 8 a.m. and lasts approximately 8 hours. Usually, it is scheduled for the day after a monitored overnight sleep study or PSG. MSLT is a better test than the maintenance of wakefulness test (see below) for demonstrating sleep-onset REM periods. This determination is important in establishing the diagnosis of narcolepsy. To ensure validity, proper interpretation of the MSLT can only be made following a PSG performed on the preceding night. Maintenance of wakefulness test (MWT). This test measures a patient’s ability to stay awake during a designated time. During the MWT, the activity of the brain, eyes, chin, and heart are monitored during four prescheduled 30-minute periods. This procedure measures a person’s ability to remain awake during sleep-inducing circumstances (i.e., sitting in a dark room). As with the MSLT, this procedure is usually conducted on the day following an overnight sleep study or PSG.

This question was answered in our Coding Essentials for RT/Pulmonary Function. For more hot topics relating to respiratory services, please visit our store or call us at 1.800.252.1578, ext. 2.

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