Doctors administer polysomnograms and multiple sleep latency tests to determine if a diagnosis of narcolepsy is appropriate, states Harvard Medical School. In some cases, physicians also perform a lumbar puncture to measure the level of hypocretin-1 in the patient's spinal fluid.
The purpose of a polysomnogram is to monitor the patient's brain waves, breathing, muscle tone and eye movements for signs of narcolepsy while the patient sleeps through a full night, explains Harvard Medical School. The doctor is also able to review the results of the study for indicators of other sleep disorders, such as sleep apnea, that may be contributing to the patient's symptoms. A multiple sleep latency test requires the patient to take a 20-minute, or longer, nap every two hours, so the doctor administering the study can observe how long it takes the patient to drift asleep each time. The doctor usually has the patient complete the multiple sleep latency test the day after the polysomnogram, so he can gauge whether the quality of the previous night's sleep has any effect on napping patterns during the day.
The hypocretin-1 spinal tap test is very efficient at confirming a diagnosis of narcolepsy because there are almost no other medical conditions that result in low levels of the chemical, notes Harvard Medical School. The test is especially useful when a patient is unable to discontinue a medication with the potential to skew sleep study results.