How is hypocretin deficiency tested in patients suspected of narcolepsy?

Testing for hypocretin deficiency in patients suspected of narcolepsy primarily involves measuring cerebrospinal fluid (CSF) levels. Hypocretin, also known as orexin, is a neuropeptide that plays a critical role in regulating wakefulness and sleep. In individuals with narcolepsy, especially type 1 narcolepsy, there is a significant reduction in the levels of hypocretin in the CSF.

The CSF analysis is performed through a lumbar puncture, allowing healthcare providers to directly assess the concentration of hypocretin-1. Low levels of hypocretin-1 are an important diagnostic criterion and help confirm the diagnosis of narcolepsy, distinguishing it from other sleep disorders.

Other methods such as blood tests, sleep studies, and urine tests are helpful in the overall assessment and diagnosis of sleep disorders but do not specifically measure hypocretin levels. Blood tests are not suitable since hypocretin does not cross the blood-brain barrier, and although sleep studies can help to identify sleep architecture changes typical in narcolepsy, they cannot provide information on hypocretin levels. Urine tests lack sensitivity for detecting hypocretin deficiency and are not used for this purpose. Therefore, measuring CSF levels is the