Antiphospholipid Syndrome

Antiphospholipid Syndrome

Antiphospholipid antibody syndrome (APS) is an autoimmune disorder in which patients have autoantibodies to phospholipid-bound proteins (eg, beta2-glycoprotein I, prothrombin, annexin A5). The pathophysiology is not precisely known.

Antiphospholipid Syndrome (APS) is an important recognised cause of acquired treatable thrombophilia. It is characterised by the core clinical manifestations of thrombosis in both venous and arterial circulation resulting in recurrent thrombotic events, thrombocytopenia, and in women, it can also be associated with recurrent pregnancy losses and a major cause of pregnancy morbidity. Because thrombosis in APS can occur at almost any site, it is a condition that is seen in almost all medical specialities.

APS occurs either as a primary condition or in the setting of an underlying systemic autoimmune disease, particularly systemic lupus erythematosus (SLE).

The precise mechanism of thrombosis in patients with autoantibodies to phospholipid-bound beta2-glycoprotein I is unknown. Annexin A5 may bind to phospholipid membrane constituents to prevent the cell membrane from initiating the activation of coagulation. If autoantibodies displace annexin A5, procoagulant endothelial cell surfaces may be exposed and provoke arterial or venous thromboses.

Results of in vitro clotting tests may paradoxically be prolonged because the autoantibodies to phospholipid-bound proteins interfere with coagulation factor assembly and activation on the phospholipid components added to plasma to initiate the tests. The lupus anticoagulant is an autoantibody that binds to phospholipid-bound protein complexes. It was initially recognized in patients with systemic lupus erythematosus (SLE), but these patients now account for only a minority of people with the autoantibody.

Other symptoms of venous or arterial thrombosis may also develop. Patients with autoantibodies to phospholipid-bound prothrombin may have levels of circulating prothrombin that is low enough to increase the risk of bleeding. Some patients have thrombocytopenia.

In a small proportion of patients with APS, widespread thromboses occur in small vessels supplying multiple organs, often causing neurologic defects. This syndrome is called catastrophic APS (CAPS) and can be confused with disseminated intravascular coagulation (DIC), heparin-induced thrombocytopenia (HIT), and thrombotic microangiopathy (TMA). Its treatment includes high-dose corticosteroids, anticoagulation, plasmapheresis, and sometimes rituximab or eculizumab.

Clinical manifestations of APS:

  • Superficial and deep vein thrombosis, cerebral venous thrombosis, retinal vein thrombosis.
  • Signs and symptoms of intracranial hypertension, pulmonary emboli, pulmonary arterial hypertension, and Budd-Chiari syndrome.
  • Livedo reticularis.
  • Arterial thrombosis – migraines, cognitive dysfunction, transient ischemic attacks, stroke, myocardial infarction, ischemic leg ulcers, digital gangrene, avascular necrosis of bone, retinal artery occlusion, renal artery stenosis, and, infarcts of spleen, pancreas, and adrenals.
  • Premature atherosclerosis – a rare feature of APS.
  • Coombs-positive hemolytic anemia and thrombocytopenia.
  • Libman-Sacks endocarditis.
  • The fetal loss does not appear to be explained by thrombosis, but rather seems to stem from antibody-mediated interference with the growth and differentiation of trophoblasts, leading to a failure of placentation.
  • Discontinuation of therapy, major surgery, infection, and trauma may trigger Catastrophic APS. Livedo ReticularisAntiphospholipid Syndrome

One clinical + one laboratory criterion:

Clinical criteria:

  • Vascular thrombosis in any tissue or organ.
  • Pregnancy morbidity: One or more unexplained deaths of a morphologically normal fetus at or beyond the tenth week of gestation, One or more premature births of a morphologically normal neonate before the thirty-fourth week of gestation because of eclampsia, severe preeclampsia, or placental insufficiency, A 3 or more unexplained consecutive spontaneous abortions before the 10th week of gestation.

Laboratory criteria:

Characteristic laboratory abnormalities in APS include persistently elevated levels of IgG and IgM antibodies directed against membrane anionic phospholipids or their associated plasma proteins or evidence of a circulating anticoagulant.

The confirmed presence of a repeated antiphospholipid (aPL) antibodies – at intermediate or high titres on two or more occasions, 12 weeks apart is a required criterion for the diagnosis of APS:

  • Antibodies against cardiolipin – ACL.
  • Antibodies against beta 2 glycoprotein I – B2GPI.
  • Lupus anticoagulant – LA.

The lupus anticoagulant (LA) is suspected if the APTT is prolonged and does not correct immediately upon 1:1 mixing with normal plasma but does return to normal upon the addition of an excessive quantity of phospholipids (done in the clinical pathology laboratory). Antiphospholipid antibodies in patient plasma are then directly measured by immunoassays of IgG and IgM antibodies that bind to phospholipid/beta2-glycoprotein I complexes on microtiter plates.


After the first thrombotic event, patients should be placed on warfarin for life aiming to achieve an INR ranging from 2.5 to 3.5, alone or in combination with 75 mg of aspirin daily.

Pregnancy morbidity is prevented by a combination of Heparin e.g. enoxaparin with Aspirin 75 mg daily. Intravenous immunoglobulin 400 mg/kg daily for 5 days may also prevent abortions, while glucocorticoids are ineffective.

Aspirin 75 mg daily protects patients with SLE positive for aPL antibodies from developing thrombotic events.

It is not yet known if the newer oral anticoagulants that inhibit either thrombin (dabigatran) or factor Xa (eg, rivaroxaban, apixaban) can be used in place of heparin or warfarin for this disorder.

Many patients with coexisting SLE are also treated with hydroxychloroquine (HCQ), which may have some benefit for patients at risk for complications of APS.

Warfarin is contraindicated in pregnancy, as it passes through the placental barrier and may cause bleeding in the fetus; warfarin use during pregnancy is commonly associated with spontaneous abortion, stillbirth, neonatal death, and preterm birth.


Antiphospholipid syndrome (APS), also known as ‘Hughes Syndrome’ or ‘sticky blood syndrome’, is an autoimmune disorder characterized by the presence of antiphospholipid antibodies which cause blood platelets to clump together. These antibodies mistakenly attack normal proteins in the blood, leading to an increased risk of blood clots forming in veins and arteries. This can result in various complications, such as deep vein thrombosis (DVT), pulmonary embolism (PE), heart attacks, strokes, and recurrent miscarriages in pregnant women. Hughes syndrome is named after Dr. Graham Hughes, a rheumatologist who first described the condition in the 1980s. People with certain autoimmune diseases, such as systemic lupus erythematosus (SLE), are at increased risk of having Hughes syndrome. There is no cure, but medical treatment can ease symptoms and reduce the risk of complications. Treatment typically involves blood-thinning medications to prevent clot formation and manage associated symptoms.


Joel L. Moake, MD. Antiphospholipid Antibody Syndrome (APS) – Hematology and Oncology – MSD Manual Professional Edition

Rabih Nayfe, Imad Uthman, Jessica Aoun, et al. Seronegative antiphospholipid syndrome, Rheumatology (Oxford) (2013) 52 (8): 1358- 1367. Accessed: February 2013.

Omar El-Gaby, MD FRCP (2010). ‘Are there evidence-based strategies in the treatment of Antiphospholipid Syndrome in pregnancy?’ MSc dissertation in Rheumatology, Hammersmith Hospital, University of London.

Negrini S, Pappalardo F, Murdaca G, Indiveri F, Puppo F. The antiphospholipid syndrome: from pathophysiology to treatment. Clin Exp Med. 2016 Jun 22.

Hughes syndrome.

Prevention of recurrent thrombosis in the antiphospholipid antibody syndrome: How long and how high with oral anticoagulant therapy? 2004, Medical Journal of Australia, vol. 180, no. 9, pp. 436–437.


Antiphospholipid syndrome, APS symptoms, Antiphospholipid antibodies, APS treatment, Blood clotting disorder, Lupus anticoagulant, Hughes syndrome, APS diagnosis, Antiphospholipid syndrome management, APS complications, sticky blood syndrome.

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  • Sangita

    My daughter is 15. She is constantly tired and sleeps 13-14 hours a day. She gets headache, dizziness sometimes, also chest pains and shortness of breath.
    She is slightly low on iron but not anemic.
    My concern is her APTT is 34.4 (22.1-27.6), platelets are 444 (150-400). She has not been tested for lupus anticoagulant or other factor deficiency. Anticardiolipin IgG and IGM were negative. I’m really concern. Please help if you can.

  • Sangita

    Hello Doctor,
    Thank you for your reply. We checked and she has lupus anticoagulant detected in her blood. She also has DRVVT test ratio 1.43 (0.80-1.20), Ratio correction 27.3 (0-10.0),DRVVT corrected ratio 1.23 (0.80-1.20) APTT 30.5 (22.1-27.6), platelets were 444, calcium 2.61(2.20-2.60), albumin 53(32-45).
    INR 0.97(0.9-1.2)

    With her symptoms of shortness of breath and chest pain, palpitations, some headaches and dizziness. I’m very sure her symptoms are from antiphospholipid syndrome. Paediatrician was not concerned and says she is clinical stable, but I am a pharmacist and I know these symptoms , however intermittent, can not be ignored and she is far from stable.

    Would you please let me know your thought.

    Many Thanks in advance

  • Lisa

    I just tested positive for lupus anticoagulant and I also have Lupus SLE. I asked my rheumatologist to run the test after a left hip AVN as I suspect a blood clotting disorder may be the culprit. My rheumatologist advises I simply take a low dose baby aspirin. Should I follow up with my hematologist for further testing and treatment?

    • Hi Lisa,
      Thank you for your comment.
      You haven’t mentioned if you had any previous blood clots and/or miscarriages or not?
      However, I would agree with your rheumatologist to keep on a low dose Aspirin (75mg once daily) and to check your blood for:
      *Antibodies against Cardiolipin – ACL.
      *Antibodies against beta 2 glycoprotein I – B2GPI.
      * And to repeat the Lupus anticoagulant test – LA.

  • Rebecca

    Hello Doctor,

    I was diagnosed with APS 13 yrs ago when I had a stillbirth. I am concerned if the COVID vaccines (which utilize the spike protein) would put me at risk for clotting from the vaccine. Many papers are pointing to activation of ACL from covid with clotting as a result. I know the spike protein elicits the immune response but will it elicit clotting with APS. the EU is investigating the Astrazeneca vaccine due to morbidities in some with clotting. Not sure where to go from here. I don’t have a hematologist and have been healthy since my APS was transient. Please advise.

    thank you

    • Hi Rebecca,
      Thanks for your comment.
      The dilemma around COVID 19 vaccines and their possible side effects are still ongoing and no one can tell you with confidence their long-term sequences. However, if you don’t have any previous thromboembolic events and you are on Aspirin it would be logical to get vaccinated.

  • Jordan

    Dr. Abdou:

    This site is a great resource, thank you!

    Coincidentally a couple days after my first Covid-19 vaccine (Moderna), I saw a rheumatologist to investigate my ongoing chronic myalgia. He did a comprehensive workup that included tests for antiphospholid antibodies – my B2GP1 IGG antibodies were very elevated (196 CU), all other antibodies normal. Follow-up testing 3 months later (2 months after my second vaccine) showed these antibodies had fallen back to reference range (<6 CU).

    The rheumatologist brushed off my question about the vaccine possibly being responsible, but given the timing and known instances of certain vaccines and some illnesses (including Covid-19) causing transient increases in antiphospholid antibodies, I find it hard to believe this was just a coincidence. I've also seen a couple of recent articles in the literature acknowledging a possible link and calling for further research (Cytokine Growth Factor Rev. 2021;60:52-60. doi:10.1016/j.cytogfr.2021.05.001 and Rheumatol Adv Pract. 2021;5(3):rkab096. Published 2021 Dec 1. doi:10.1093/rap/rkab096).

    Even though I didn't have any known events at that time, my understanding is that a high-level of those antibodies is in and of itself a risk factor for developing clots. I'm far from an antivaxxer, but this certainly gives me pause when considering whether or not to get a booster shot.

    • Hi Jordan,
      Many thanks for your comment and your kind words on my website.
      It is not clear from your comment whether you had a full antiphospholipid screen including the lupus anticoagulant and cardiolipin antibodies or just the B2GP1 IgG and IgM antibodies? We still don’t know too much about the short and long-term complications of the Coronavirus and the available vaccinations for it but blood clots are mainly linked to the AstraZeneca Vaccine rather than to Moderna. I agree with you that your first high B2GP1 IgG reading could be reactive but I would suggest having another full antiphospholipid screen as part of investigating your ongoing chronic myalgia and going ahead with your booster dose of COVID-19 vaccination (likely Pfizer) regardless of the result of the antiphospholipid screen in view of the rapidly spreading Omicron variant.

  • Jenni

    I tested positive 12 weeks apart for the antiphospholipid antibody. My rheumatologist said unless an event occurs to not take baby aspirin or get on a blood thinner. I had 2 miscarriages about 14 years ago I believe they were before 10 weeks. Is this the best course of action or should I see a hematologist about taking something. Thanks!

    • Hi Jenni,
      Thank you for reaching out.
      Have you experienced any thromboembolic events before or do you have a family history of blood clots?
      If you are considering having a baby, it is important to discuss with your treating doctor regarding your Antiphospholipid Syndrome (APS) treatment plan.
      Treatment during pregnancy typically includes daily doses of baby aspirin and low molecular weight heparin.
      I recommend consulting with a hematologist for further guidance.
      Best regards,
      Dr. M Abdou

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