| 1. Evidence of involvement of 3 or more organs, systems, and/or tissues |
| 2. Development of manifestations simultaneously or in <1 week |
| 3. Confirmation by histopathology of small-vessel occlusion in at least 1 organ or tissue (vasculitis may coexist, but significant thrombosis must be present) |
| 4. Laboratory confirmation of the presence of antiphospholipid antibodies (two positive serologies at least 6 weeks apart) |
| Definite CAPS |
| All 4 criteria are present |
| Probable CAPS |
| All 4 criteria are present, except only 2 organs, systems, and/or tissues are involved |
| All 4 criteria are present, except for the absence of laboratory confirmation of antiphospholipid antibodies |
| Only criteria 1, 2, and 4 are met |
| Only criteria 1, 3, and 4 are met, with development of a third event more than 1 week from but within 1 month of presentation, despite anticoagulation |
| 1. Evidence of involvement of 3 or more organs, systems, and/or tissues |
| 2. Development of manifestations simultaneously or in <1 week |
| 3. Confirmation by histopathology of small-vessel occlusion in at least 1 organ or tissue (vasculitis may coexist, but significant thrombosis must be present) |
| 4. Laboratory confirmation of the presence of antiphospholipid antibodies (two positive serologies at least 6 weeks apart) |
| Definite CAPS |
| All 4 criteria are present |
| Probable CAPS |
| All 4 criteria are present, except only 2 organs, systems, and/or tissues are involved |
| All 4 criteria are present, except for the absence of laboratory confirmation of antiphospholipid antibodies |
| Only criteria 1, 2, and 4 are met |
| Only criteria 1, 3, and 4 are met, with development of a third event more than 1 week from but within 1 month of presentation, despite anticoagulation |