Algorithm A.

Catastrophic antiphospholipid syndrome (CAPS) diagnosis in patients with history of antiphospholipid syndrome (APS) or persistent antiphospholipid antibody (aPL) positivity [Erkan et al. 2010]. Reprinted from [Erkan et al. 2010] with permissions from Elsevier.

*Our recommendation for the definition of ‘positive aPL’ is: lupus anticoagulant (LA) test positive based on the guidelines of International Society of Thrombosis and Haemostasis [Pengo et al. 2009]; anticardiolipin antibody (aCL) IgG/M ≥40 U, and/or anti-β₂-glycoprotein-I antibody (aβ2GPI) IgG/M ≥40 U. Caution and further assessment(s) are required if: (a) LA test is performed in anticoagulated patients; (b) aCL or aβ2GPI IgG/M titers are in the range of 20–39 U; and/or (c) aCL or aβ2GPI IgA is the only positive aPL enzyme-linked immunosorbent assay (ELISA) test.