Rule out means the diagnosis is still a possibility, but the psychiatrist can't positively make the diagnosis because he needs more time to observe.
Both J and A have a rule out on BiPolar (BP). In my son's case, the psychiatrist suspects he has BiPolar (BP) and is treating him as such, but he doesn't want to make a firm diagnosis until my son gets to the other side of puberty. In my daughter's case, the psychiatrist hasn't decided yet whether she had an idiosynchratic reaction to an SSRI (and would do fine with other SSRIs) or whether her reaction was the start of BiPolar (BP).
Does M have a rule out on a diagnosis?
