The classification criteria for identifying catastrophic antiphospholipid syndrome (APS) rely on four diagnostic markers, which involve symptom presentation and laboratory results. These criteria include:

- Evidence showing involvement of three or more organs, systems, or tissues.
- Simultaneous or concurrent manifestations occurring within one week.
- Small vessel occlusion confirmed by histopathology in at least one organ or tissue.
- Presence of positive antiphospholipid antibodies, such as lupus anticoagulant or anticardiolipin.

The algorithm assesses which of these criteria are met to determine the likelihood of catastrophic APS. The evaluation is systematic, considering the following conditions and their respective interpretations:

| Criteria Satisfied          | Interpretation                       |
|-----------------------------|--------------------------------------|
| All four criteria (A, B, C, D) are met | Definite catastrophic APS           |
| Criteria A, B, and D are met          | Probable catastrophic APS           |
| Any other combination                 | Diagnostic criteria are not met     |

To calculate, the algorithm reviews each input condition as follows:

- Condition A is met if there is evidence of involvement of three or more organs, systems, or tissues.
- Condition B is met if symptoms are simultaneous or occur within one week.
- Condition C is confirmed if histopathology shows small vessel occlusion.
- Condition D is met if there are positive results for antiphospholipid antibodies.

The categorization process starts by checking if all four criteria are satisfied. If they are, the diagnosis is "Definite catastrophic APS." If only criteria A, B, and D are fulfilled, with exclusion of C, the result is "Probable catastrophic APS." Any other combination of criteria signifies that the diagnostic criteria for catastrophic APS are not met. This approach ensures a structured assessment based on the specific combination of symptoms and laboratory evidence.

The Classification Criteria for Catastrophic Antiphospholipid Syndrome (CAPS) is a diagnostic tool designed to identify patients with this severe variant of antiphospholipid syndrome. The target patient population includes individuals presenting with multi-systemic clinical manifestations suggestive of thrombotic microangiopathy.

The primary components of the classification criteria include evidence of involvement of three or more organs, systems, and/or tissues; simultaneous or concurrent manifestations within one week; small vessel occlusion in at least one organ or tissue confirmed by histopathology; and the presence of antiphospholipid antibodies, specifically lupus anticoagulant and/or anticardiolipin.

The classification of CAPS is determined by the combination of these components. Definite CAPS is diagnosed if all four components are present. Probable CAPS is diagnosed if there is evidence of multi-systemic involvement, simultaneous or concurrent manifestations within one week, and the presence of antiphospholipid antibodies, but without histopathological confirmation of small vessel occlusion. If these criteria are not met, the diagnosis of CAPS is not established.

This classification system aids in the timely identification of CAPS, which is crucial given the high morbidity and mortality associated with this condition. It also assists in differentiating CAPS from other thrombotic microangiopathies, thereby guiding appropriate management strategies.

Classification criteria for catastrophic antiphospholipid syndrome