Antiphospholipid Syndrome (APS)

Medically Reviewed on 5/3/2023

What is antiphospholipid syndrome (APS)?

Antiphospholipid syndrome is a disorder of the immune system that is characterized by excessive clotting of blood and/or certain complications of pregnancy (premature miscarriages, unexplained fetal death, or premature birth) and the presence of antiphospholipid antibodies (such as anti-cardiolipin or lupus anticoagulant antibodies) in the blood.

Clotting disorders associated with antiphospholipid syndrome include strokeblood clots deep within the legs (deep venous thrombosis, or DVT) and clots in the lungs (pulmonary embolism, or PE). Patients with antiphospholipid syndrome have both blood clots and antiphospholipid antibodies that are detectable with blood testing.

Antiphospholipid syndrome is also called phospholipid antibody syndrome, cardiolipin antibody syndrome, and Hughes syndrome in honor of the doctor who first described it.

What causes antiphospholipid syndrome?

The cause of antiphospholipid syndrome is not completely known. Antiphospholipid antibodies reduce the levels of annexin V, a protein that binds phospholipids and has potent clot-blocking (anticoagulant) activity. The reduction of annexin V levels is thought to be a possible mechanism underlying the increased tendency of blood to clot and the propensity to pregnancy loss characteristic of the antiphospholipid syndrome. Certain genes may be risk factors for the development of antiphospholipid syndrome.

Antiphospholipid antibodies, such as anticardiolipin, have also been associated with decreased levels of prostacyclin, a chemical that prevents the clumping together of normal blood clotting elements called platelets.

It is important to note that antiphospholipid antibodies can also be found in the blood of individuals without any disease process. In fact, antiphospholipid antibodies have been reported in a small percentage of the normal population. Harmless antiphospholipid antibodies can be detected in the blood for a brief period occasionally in association with a wide variety of conditions, including bacterial, viral (hepatitis and HIV), and parasitic (malaria) infections. Certain drugs can cause antiphospholipid antibodies to be produced in the blood, including antibiotics, cocaine, hydralazine, procainamide, and quinine.

Nevertheless, the antiphospholipid antibodies (a protein) are not considered normal blood proteins and have been found to be associated with a number of illnesses. These illnesses include abnormal clotting (thrombosis) of arteries (stroke and infarction) and/or veins, premature miscarriages (spontaneous abortions), abnormally low blood platelet counts (thrombocytopenia), purplish mottling discoloration of the skin (livedo reticularis), migraine headaches, and a rare form of inflammation of the nervous tissue of the brain or spinal cord called transverse myelitis.

Researchers are recently also finding that there are patients with slowly progressive memory problems and patients with a form of "atypical multiple sclerosis" who have antiphospholipid antibodies detectable in their blood.

Diagnosis of antiphospholipid syndrome

Patients with the antiphospholipid syndrome can have a variety of antibodies to molecules called phospholipids in their blood. These antibodies include VDRL/RPR (a syphilis test that can be falsely positive in these patients), lupus anticoagulant, prolonged PTT, beta 2 glycoprotein I antibodies, and anticardiolipin antibody. As mentioned above, the anticardiolipin antibody has also been found in patients with the immune disease systemic lupus erythematosus, which is characterized by the production of a variety of abnormal antibodies.

What is the treatment for antiphospholipid syndrome?

The treatment of patients with anticardiolipin syndrome has substantially evolved since cardiolipin antibodies were noted to be clinically important in the mid-1980s. Each manifestation of the antiphospholipid syndrome, and each individual patient with the condition, is treated uniquely.

Because many of the features of illness with anticardiolipin syndrome are associated with an abnormal grouping of normal blood clotting elements (platelets), treatment is often directed toward preventing clotting by thinning the blood. Patients with this disorder have a tendency to form blood clots (thrombosis). The unwanted blood clotting can affect the function of virtually any organ. Medications that thin (anticoagulate) the blood, such as heparin (Hep-Lock, Liquaemin, Lovenox) and warfarin (Coumadin), are powerful blood thinners that are used for treatment. Aspirin has an effect on platelets that inhibits their grouping (aggregation) and has also been used in low doses to thin the blood of selected patients with less severe disease. Cortisone-related medications, such as prednisone, have been used to suppress the immune activity and inflammation in patients with certain features of the condition. For patients with systemic lupus erythematosus who also have antiphospholipid syndrome, hydroxychloroquine (Plaquenil) has been reported to add some protection against blood clotting.

Other reported treatments include the use of intravenous gamma globulin for selected patients with histories of premature miscarriage and those with low blood-clotting elements (platelets) during pregnancy. Recent research studies, however, suggest that intravenous gamma globulin may be no more effective than a combination of aspirin and heparin.

The treatment of antiphospholipid antibody syndrome during pregnancy typically involves low dose aspirin and low molecular weight heparin (Lovenox). Additionally, intravenous immunoglobulins have been infused, but their effectiveness is not proven.


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Complications and catastrophic antiphospholipid syndrome

Catastrophic antiphospholipid syndrome (CAPS) is a variant of antiphospholipid syndrome that is characterized by blockage of many blood vessels throughout the body. As a result of catastrophic antiphospholipid syndrome, many organs can be affected, including the skin, lungs, brain, heart, kidneys, and bowels. Catastrophic antiphospholipid syndrome is treated with anticoagulation, corticosteroids (cortisone medication), and plasmapheresis (plasma exchange).

Catastrophic antiphospholipid syndrome is rare. Catastrophic antiphospholipid syndrome is sometimes referred to as Asherson's syndrome after the researcher who described it in the early 1990s.

What is the prognosis for antiphospholipid syndrome?

The prognosis of antiphospholipid syndrome depends on the character and the intensity of its manifestations. Earlier treatment will tend to have better outcomes.

Is it possible to prevent antiphospholipid syndrome?

If a person is already known to have phospholipid antibodies, it is possible to prevent antiphospholipid syndrome with methods that decrease the chances of blood clotting, including aspirin and/or heparin. Hydroxychloroquine (Plaquenil) may have some preventative benefits for selected patients.

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Medically Reviewed on 5/3/2023
John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care

Bucciarelli S., et al. "Mortality in the Catastrophic Antiphospholipid Syndrome." Arthritis & Rheumatism (2006): 2568-2576.

Pisetsky, David S., and Peter H Schur. "Diagnosis of the antiphospholipid syndrome." Sept. 17, 2014. <>.

Ruddy, Shaun, eds., et al. Kelley's Textbook of Rheumatology. Philadelphia: WB Saunders Co., 2000.