Measuring orexin (hypocretin) levels
Many cases of narcolepsy are linked to a deficiency in the sleep-regulating brain chemical orexin (also known as hypocretin).
Recent research has shown that measuring the level of orexin in your cerebrospinal fluid (which surrounds the brain and spinal cord) can be useful in diagnosing narcolepsy, and this test is increasingly being used by sleep disorder specialists to help make a diagnosis.
To measure your level of orexin, a sample of your cerebrospinal fluid is removed using a needle during a procedure called a lumbar puncture.