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PubMed This is a summary of 23 peer-reviewed journal articles Updated
Rheumatology

Symptoms, Subtypes, and the Biology of APS

At a Glance

Antiphospholipid Syndrome (APS) is an autoimmune condition that increases the risk of blood clots and pregnancy complications. It can occur on its own (primary) or alongside conditions like lupus (secondary). Knowing the symptoms helps patients monitor for severe complications.

To navigate life with Antiphospholipid Syndrome (APS), it helps to understand how the condition interacts with your body. APS is not just a “clotting disorder”; it is a complex immune process where your body produces antibodies that target phospholipids (fats that make up cell membranes) and proteins like beta-2 glycoprotein I [1][2]. This interaction activates your blood vessels and immune cells, creating a “pro-clotting” environment [3][4].

Primary vs. Secondary APS

Doctors divide APS into two main categories based on whether it appears alone or alongside another condition:

  • Primary APS: This is when APS occurs on its own, without any other underlying autoimmune disease [5].
  • Secondary APS: This occurs when APS is associated with another autoimmune condition, most commonly Systemic Lupus Erythematosus (SLE) [6]. Patients with secondary APS may have more complex immune profiles and a higher risk of organ involvement, making close monitoring by a rheumatologist essential [6][7].

Common and “Hidden” Symptoms

While blood clots (thrombosis) and pregnancy complications are the hallmarks of APS, the condition can affect the body in several other ways.

Thrombotic and Obstetric Symptoms

  • Vascular Events: The most common signs are Deep Vein Thrombosis (DVT—pain or swelling in one leg), Pulmonary Embolism (PE—sudden shortness of breath or chest pain), and strokes or “mini-strokes” (TIA) [8][9].
  • Pregnancy Complications: This includes recurrent miscarriages (often before the 10th week), late-term pregnancy loss, or early delivery due to preeclampsia (dangerously high blood pressure) [10][11].

Non-Thrombotic Manifestations

APS can also cause symptoms that aren’t caused by a single large clot:

  • Livedo Reticularis: A purple, lace-like pattern on the skin, often most visible on the legs or arms [12].
  • Thrombocytopenia: A low level of platelets (the cells that help blood clot), which may surprisingly be found in a condition that causes too much clotting [13].
  • Cardiac Valve Disease: Thickening or “vegetations” on heart valves (known as Libman-Sacks endocarditis) that can affect blood flow [14][15].

Rare but Serious: Catastrophic APS (CAPS)

Catastrophic Antiphospholipid Syndrome (CAPS) is an extremely rare but life-threatening complication occurring in less than 1% of APS patients [16]. It involves widespread clotting in the smallest blood vessels, leading to failure of multiple organs (like the kidneys, lungs, or brain) simultaneously [17][18].

Warning Signs (Red Flags):

  • Sudden, severe symptoms involving multiple parts of the body (e.g., confusion, shortness of breath, and decreased urination) [19].
  • A rapid drop in your platelet count [20].

CAPS is often triggered by an infection, surgery, or stopping your blood thinner medication [21][22]. Knowing these triggers allows you to work with your care team to take extra precautions during high-risk times, such as using “bridging” therapy during surgery. Most patients never experience CAPS, but being aware of the “red flags” ensures you can seek immediate medical attention if needed [23].

For more context on what to expect at the laboratory, proceed to the Diagnosis, The 12-Week Rule, and Understanding Your Labs section.

Common questions in this guide

What is the difference between primary and secondary APS?
Primary APS occurs on its own without any other autoimmune disease. Secondary APS occurs alongside another autoimmune condition, most commonly systemic lupus erythematosus (SLE).
Can APS cause symptoms other than blood clots?
Yes, APS can cause a purple lace-like skin pattern called livedo reticularis, low blood platelet levels, and thickening of the heart valves. It is also strongly linked to recurrent miscarriages and high blood pressure during pregnancy.
What is Catastrophic Antiphospholipid Syndrome (CAPS)?
CAPS is a very rare, life-threatening complication where widespread blood clots form in the smallest blood vessels, causing multiple organs to fail simultaneously. It occurs in less than one percent of patients with APS and requires immediate emergency care.
What are the warning signs of CAPS?
Warning signs of CAPS include sudden confusion, severe shortness of breath, decreased urination, and a rapid drop in blood platelets. These emergencies are often triggered by an infection, surgery, or stopping blood thinner medication.
How does APS affect pregnancy?
APS increases the risk of recurrent miscarriages, typically before the tenth week of pregnancy. It can also lead to late-term pregnancy loss or require early delivery due to preeclampsia, a dangerously high blood pressure condition.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Do I have primary APS or secondary APS associated with Lupus (SLE)?
  2. 2.Have you checked my heart valves for thickening or my skin for livedo reticularis?
  3. 3.If I develop an infection or need surgery, what specific steps should we take to prevent a 'second hit' or CAPS?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (23)
  1. 1

    Anti-β2 glycoprotein domain 1 antibody as a diagnostic marker for antiphospholipid syndrome and a predictor of thrombosis: a systematic review and meta-analysis.

    Li L, Chen J, Feng J, et al.

    Frontiers in immunology 2025; (16()):1541165 doi:10.3389/fimmu.2025.1541165.

    PMID: 40336949
  2. 2

    Platelet-derived microparticles stimulated by anti-β2GPI/β2GPI complexes induce pyroptosis of endothelial cells in antiphospholipid syndrome.

    Di L, Zha C, Liu Y

    Platelets 2023; (34(1)):2156492 doi:10.1080/09537104.2022.2156492.

    PMID: 36550078
  3. 3

    TO SHOw how we have been ENgaged in the APS FiELD (What we learned on APS collaborating with Professor Yehuda Shoenfeld).

    Meroni PL, Borghi MO, Raschi E, et al.

    Autoimmunity reviews 2024; (23(9)):103613 doi:10.1016/j.autrev.2024.103613.

    PMID: 39216616
  4. 4

    Release of neutrophil extracellular traps by neutrophils stimulated with antiphospholipid antibodies: a newly identified mechanism of thrombosis in the antiphospholipid syndrome.

    Yalavarthi S, Gould TJ, Rao AN, et al.

    Arthritis & rheumatology (Hoboken, N.J.) 2015; (67(11)):2990-3003 doi:10.1002/art.39247.

    PMID: 26097119
  5. 5

    Autoimmune haemolytic anaemia and antiphospholipid antibodies in paediatrics: a systematic review and meta-analysis.

    Merashli M, Arcaro A, Graf M, et al.

    Clinical rheumatology 2021; (40(5)):1967-1973 doi:10.1007/s10067-020-05436-2.

    PMID: 33006737
  6. 6

    Antiphospholipid syndrome (APS) in patients with systemic lupus erythematosus (SLE) implies a more severe disease with more damage accrual and higher mortality.

    Riancho-Zarrabeitia L, Martínez-Taboada V, Rúa-Figueroa I, et al.

    Lupus 2020; (29(12)):1556-1565 doi:10.1177/0961203320950477.

    PMID: 32807021
  7. 7

    Reduced circulating Tregs and positive pANCA were robustly associated with the occurrence of antiphospholipid syndrome in patients with systemic lupus erythematosus.

    Wang J, Guo HX, Cheng T, et al.

    Lupus 2023; (32(6)):746-755 doi:10.1177/09612033231171287.

    PMID: 37051771
  8. 8

    Added value of antiphosphatidylserine/prothrombin antibodies in the workup of thrombotic antiphospholipid syndrome: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies.

    Vandevelde A, Chayoua W, de Laat B, et al.

    Journal of thrombosis and haemostasis : JTH 2022; (20(9)):2136-2150 doi:10.1111/jth.15785.

    PMID: 35713971
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    Understanding antiphospholipid syndrome clinical phenotypes with the guidance of antiphospholipid antibody-related pathogenic mechanisms.

    Sevim E, Erton ZB, Erkan D

    Current opinion in immunology 2026; (100()):102770 doi:10.1016/j.coi.2026.102770.

    PMID: 42013510
  10. 10

    Obstetric and vascular antiphospholipid syndrome: same antibodies but different diseases?

    Meroni PL, Borghi MO, Grossi C, et al.

    Nature reviews. Rheumatology 2018; (14(7)):433-440 doi:10.1038/s41584-018-0032-6.

    PMID: 29891914
  11. 11

    Trophoblast Cell Function in the Antiphospholipid Syndrome.

    Vrzić Petronijević S, Vilotić A, Bojić-Trbojević Ž, et al.

    Biomedicines 2023; (11(10)) doi:10.3390/biomedicines11102681.

    PMID: 37893055
  12. 12

    Analysis of Serbian Primary Antiphospholipid Syndrome Patients Confirmed a Strong Association Between Livedo Reticularis and Arterial Thrombosis: A National Cross-Sectional Cohort Study.

    Djokovic A, Stojanovich L, Stanisavljevic N, et al.

    Journal of clinical rheumatology : practical reports on rheumatic & musculoskeletal diseases 2022; (28(7)):362-366 doi:10.1097/RHU.0000000000001879.

    PMID: 35697016
  13. 13

    Performance validation of the 2023 American College of Rheumatology/European League Against Rheumatism antiphospholipid syndrome classification criteria in an antiphospholipid syndrome cohort.

    Zhao Y, Huang C, Zhou Y, et al.

    Journal of thrombosis and haemostasis : JTH 2024; (22(6)):1660-1674 doi:10.1016/j.jtha.2024.02.019.

    PMID: 38462219
  14. 14

    Antiphospholipid Antibodies Are Major Risk Factors for Non-Thrombotic Cardiac Complications in Systemic Lupus Erythematosus.

    Nagy N, Bói B, Papp G, et al.

    Biomedicines 2024; (12(3)) doi:10.3390/biomedicines12030530.

    PMID: 38540143
  15. 15

    Embolic Phenomena of Libman-Sacks Endocarditis and Antiphospholipid Syndrome.

    Gorantla A, Schaible M, Sivakumar SS, et al.

    Cureus 2023; (15(10)):e46957 doi:10.7759/cureus.46957.

    PMID: 38021689
  16. 16

    Diagnosis and Management of Catastrophic Antiphospholipid Syndrome and the Potential Impact of the 2023 ACR/EULAR Antiphospholipid Syndrome Classification Criteria.

    Jacobs L, Wauters N, Lablad Y, et al.

    Antibodies (Basel, Switzerland) 2024; (13(1)) doi:10.3390/antib13010021.

    PMID: 38534211
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    Catastrophic antiphospholipid syndrome and pregnancy. Clinical report.

    Khizroeva J, Bitsadze V, Makatsariya A

    The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians 2019; (32(12)):2091-2094 doi:10.1080/14767058.2017.1422715.

    PMID: 29284338
  18. 18

    Clinical characteristics and risk factors of microvascular involvement in primary antiphospholipid syndrome: a longitudinal single-center study in China.

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    Lupus 2019; (28(13)):1558-1565 doi:10.1177/0961203319882506.

    PMID: 31635555
  19. 19

    Catastrophic antiphospholipid syndrome refractory to high-dose intravenous immunoglobulin responsive to therapeutic plasma exchange.

    James TE, Martin LJ, Warkentin TE, Crowther MA

    Platelets 2021; (32(6)):828-831 doi:10.1080/09537104.2020.1802414.

    PMID: 32762580
  20. 20

    Thrombocytopenia in high-risk patients with antiphospholipid syndrome.

    Pontara E, Banzato A, Bison E, et al.

    Journal of thrombosis and haemostasis : JTH 2018; (16(3)):529-532 doi:10.1111/jth.13947.

    PMID: 29316193
  21. 21

    Pediatric catastrophic antiphospholipid syndrome with extensive skin involvement.

    Pradhan S, Sinha A, Dash G, Ojha V

    Pediatric dermatology 2024; (41(6)):1148-1151 doi:10.1111/pde.15642.

    PMID: 38783589
  22. 22

    Precipitating factors of catastrophic antiphospholipid syndrome: the role of anticoagulant treatment in a series of 112 patients.

    Stammler R, Nguyen Y, Yelnik C, et al.

    Journal of thrombosis and haemostasis : JTH 2023; (21(5)):1258-1265 doi:10.1016/j.jtha.2023.02.007.

    PMID: 36792010
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    Antiphospholipid Patients Admitted in the Intensive Care Unit: What Must The Rheumatologist Know?

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    PMID: 38652403

This page provides educational information about Antiphospholipid Syndrome (APS) symptoms and subtypes. Always consult your rheumatologist or care team to discuss your specific diagnosis and medical risks.

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