For individuals who develop an unexpected psychosis, there is something to be said for testing them for autoimmune antibodies. And something against. At the 36th Congress of the European College of Neuropsychopharmacology (ECNP) this week, the topic was worth a controversy session, where speakers presented the pros and cons of the approach. Currently used tests have a specificity of 99%. But as Ester Coutinho, consultant neurologist at the University of Coimbra, pointed out, the validity of diagnostic tests depends on the prevalence of the disorder one is looking for as well. Coutinho estimated that autoimmune psychoses account for 1% of psychoses overall.