How is ocd officially diagnosed?

DSM -IV: Professionals use a manual that is based on years of research and professional opinion called the diagnostic and statistical manual. This has very specific criteria for diagnosing ocd.

OCD: OCD is obsessive compulsive disorder, which is comprised of obsessions (repeating unwanted thoughts) and compulsions (ritualistic behaviors to help deal with those thoughts) such as washing hands repeatedly, constantly cleaning, checking locks, and other similar behaviors. Often the emotions behind OCD are based in fear and/or anger that is unresolved and even unverbalized.

OCD: Is an anxiety disorder characterized by intrusive thoughts that cause apprehension/fear/worry, and repetitive behaviors in attempt to reduce tension & anxiety. Examples are excess washing, cleaning, checking, hoarding, etc. Symptoms are time-consuming & cause more distress.