Diagnosis of Cyclic Vomiting Syndrome

CVS is hard to diagnose because no clear tests--such as a blood test or x ray--exist to identify it. A doctor must diagnose CVS by looking at symptoms and medical history and by excluding more common diseases or disorders that can also cause nausea and vomiting. Also, diagnosis takes time because doctors need to identify a pattern or cycle to the vomiting.

source: http://digestive.niddk.nih.gov/ddiseases/pubs/cvs/index.htm