What do I talk about when I talk about measuring CNS orexin-A? Considerations of orexin-A measurements in clinical and preclinical setting

Determination of orexin-A level in the cerebrospinal fluid is a central diagnostic tool in narcolepsy diagnostics. There is also much interest in determining the orexin levels in other disorders of sleep and wakefulness and even in completely different perspectives. Radioimmunoassay on lumbar puncture samples is the standard method for the quantitation. However, there are problems related to this method and thus recently have even mass spectrometry-based identification methods been developed for orexin-A. Unfortunately, even these have not been quite able to deliver what was expected. In this short review, I review and assess the use and the performance of each method and present the open questions and the hypotheses to answer these.