Antiphospholipid Syndrome Criteria Calculator
One clinical plus one persistent laboratory criterion classifies APS. For stroke practice this diagnosis punches above its weight: it is a leading identifiable cause of stroke under 50, it demands twelve-week-apart antibody confirmation, and — after TRAPS — it is a warfarin diagnosis, not a DOAC one.
Reviewed by Zaka Ahmed, MD Clinical reference · 4 min read
Revised Sapporo (Sydney) Criteria
APS is classified when at least one clinical criterion AND at least one laboratory criterion are met — with the laboratory finding present on two or more occasions at least 12 weeks apart.
The classification updates as you select criteria.
Educational tool only, presenting the revised Sapporo classification criteria (2006); the 2023 ACR/EULAR criteria use a weighted point system for research classification. Classification criteria are not diagnostic criteria — clinical APS can exist outside them, and management belongs with hematology/rheumatology input.
Clinical notes & interpretation Scoring guidance, pitfalls, FAQs, and references
Why the 12 weeks matter
Antiphospholipid antibodies appear transiently during infection and acute illness — including the acute stroke itself — so a single positive titer drawn in the hospital classifies nothing. The criteria demand persistence: the same antibody, twice, at least 12 weeks apart, with anticardiolipin at medium-high titer. The practical consequence for stroke workups: send the panel when the suspicion arises, but calendar the confirmatory draw before writing "APS" anywhere a future clinician will read it. Note also that lupus anticoagulant testing is unreliable on anticoagulation — time it thoughtfully.
The stroke stakes: young-adult stroke and the DOAC trap
APS is among the most important identifiable causes of ischemic stroke under 50, and stroke or TIA is its most common arterial presentation. The workup instinct: unexplained stroke in a young patient, especially with prior miscarriage history, livedo racemosa, thrombocytopenia, an unexplained prolonged aPTT, or SLE. The management point with the sharpest edge: thrombotic APS — above all the triple-positive phenotype — is treated with warfarin, not a DOAC. TRAPS was stopped early when rivaroxaban-arm patients suffered excess arterial events (strokes prominently), and guidance since advises against DOACs in high-risk APS. A young "cryptogenic" stroke patient discharged on apixaban whose APS panel later confirms is a patient whose anticoagulant needs to be changed — a follow-up loop worth building into clinic workflow.
Frequently asked questions.
Does a single positive antibody test diagnose APS?
No — persistence on two occasions at least 12 weeks apart is required, precisely because transient positivity with infection and acute illness is common.
Can patients with APS take DOACs?
Guidance advises against DOACs in high-risk (especially triple-positive, arterial-event) APS after TRAPS showed excess arterial thrombosis with rivaroxaban versus warfarin. Warfarin (INR 2–3) remains standard for thrombotic APS; any exception is a specialist decision.
What changed with the 2023 ACR/EULAR criteria?
They introduced a weighted, domain-based point system (with entry criteria) designed for research classification — more specific, more granular about antibody profiles. The Sydney framework above remains the familiar bedside skeleton; formal research classification now uses the 2023 system.
References.
- Miyakis S, Lockshin MD, Atsumi T, et al. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS). J Thromb Haemost. 2006;4(2):295–306. PubMed
- Pengo V, Denas G, Zoppellaro G, et al. Rivaroxaban vs warfarin in high-risk patients with antiphospholipid syndrome (TRAPS). Blood. 2018;132(13):1365–1371. PubMed
- Barbhaiya M, Zuily S, Naden R, et al. 2023 ACR/EULAR antiphospholipid syndrome classification criteria. Ann Rheum Dis. 2023;82(10):1258–1270. PubMed