Most common, uh, cause for acquired, uh, thrombophilia.
Antiphospholipid Syndrome (APS) is the most common cause of acquired thrombophilia.
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Here is a complete answer based on authoritative textbook sources:
Most Common Cause of Acquired Thrombophilia: Antiphospholipid Syndrome (APS)
Antiphospholipid Syndrome (APS) is the most common acquired (non-hereditary) thrombophilia.
"Antiphospholipid syndrome patients have acquired, not a genetic, thrombophilia."
- Braunwald's Heart Disease, A Textbook of Cardiovascular Medicine
What is APS?
APS is an autoimmune disorder defined by:
- Venous and/or arterial thrombosis, OR pregnancy morbidity
- In the presence of antiphospholipid antibodies (aPL)
The three key antibodies are:
- Lupus anticoagulant (LA) - most thrombogenic; paradoxically prolongs aPTT in vitro but is procoagulant in vivo
- Anticardiolipin antibodies (aCL) - IgG/IgM
- Anti-beta-2 glycoprotein I antibodies (anti-β2GPI) - IgG/IgM
"Lupus anticoagulant was initially discovered in patients with SLE and prolongation of the aPTT; however, in vivo, the lupus anticoagulant acts as a procoagulant and is associated with thrombosis."
- Tintinalli's Emergency Medicine
Diagnosis (Sapporo/Revised Criteria)
Requires BOTH of the following confirmed on two occasions at least 12 weeks apart:
| Clinical | Laboratory |
|---|---|
| Arterial/venous thrombosis | Lupus anticoagulant |
| Pregnancy morbidity (3+ miscarriages, unexplained fetal death ≥10 weeks, premature birth ≤34 weeks) | Anticardiolipin IgG/IgM (>40 units) |
| Anti-β2GPI IgG/IgM (>99th percentile) |
Key Epidemiology
- APS affects approximately 40-50 per 100,000 persons
- aPL antibodies are positive in ~13% of patients with stroke, ~11% with MI, ~9.5% with DVT
- Up to 5% of healthy young people have aPL antibodies, but only a minority develop full APS
- More common in women; associated with SLE in secondary APS
Primary vs. Secondary APS
| Type | Description |
|---|---|
| Primary APS | No underlying condition (majority of cases) |
| Secondary APS | Associated with SLE, other autoimmune/rheumatologic disorders, infections, or drugs (phenytoin, hydralazine, cocaine) |
Catastrophic APS (CAPS)
About 1% of APS patients develop CAPS - rapid widespread small-vessel occlusion in multiple organs.
- Triggers: infection, surgery, OCP withdrawal, anticoagulant withdrawal
- Mortality ~50% despite treatment
- Management: anticoagulation + steroids + immunosuppressives + plasmapheresis ± IVIg
Management
- Recurrent thrombosis: Lifelong anticoagulation (warfarin is traditional; NOACs are increasingly used but with caution - warfarin preferred in triple-positive aPL)
- Pregnancy with APS: LMWH or UFH + low-dose aspirin
- Asymptomatic aPL positivity alone: Prophylaxis is NOT recommended (requires personal history of thrombosis)
Important Distinction
| APS (Acquired) | Factor V Leiden (Inherited) | |
|---|---|---|
| Type | Acquired autoimmune | Genetic (autosomal dominant) |
| Thrombosis type | Both arterial AND venous | Venous predominantly |
| Most common overall | Most common acquired thrombophilia | Most common inherited thrombophilia |
Note: Factor V Leiden is the most frequently diagnosed thrombophilia overall (including inherited), but APS is the most common acquired thrombophilia specifically.
Sources: Tintinalli's Emergency Medicine; Braunwald's Heart Disease; Goldman-Cecil Medicine; Scott-Brown's Otorhinolaryngology; Henry's Clinical Diagnosis and Management by Laboratory Methods
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