The catastrophic antiphospholipid syndrome (APS) is the most severe form of APS with acute multiple organ involvement and small vessel thrombosis. During the 13th International Congress on Antiphospholipid Antibodies (aPL) a "Catastrophic APS Task Force" was developed to discuss the challenges in the diagnosis and management of catastrophic APS. The purpose of this paper is to summarize the diagnostic challenges (false-positive/negative aPL results and overlap with other thrombotic microangiopathies) and propose updated diagnostic algorithms for catastrophic APS. Important steps of the diagnostic algorithms include: a) history of APS or persistent aPL-positivity; b) three or more organ new thrombosis developing in less than a week; c) biopsy diagnosis of microthrombosis; and d) other explanations for multiple organ thromboses and/or microthrombosis.
