Antiphospholipid Syndrome

Antiphospholipid antibody syndrome (APS) is an autoimmune disease mostly affecting women between ages 30 and 40. In APS, abnormal proteins (aPL) can cause the formation of blood clots in veins and arteries. Clots may cause miscarriage, harm a fetus, or lead to heart attacks, strokes, kidney damage, or pulmonary embolism. In severe cases, multiple organs may be affected at the same time. About 40% of systemic lupus erythematosus (SLE) patients also test positive for antiphospholipid antibodies, but only a few develop blood clots.

What Are the Signs/Symptoms?

APS may not be detected until an individual has unexpected problems caused by blood clots, such as repeated miscarriages, pulmonary embolism, or a heart attack. To screen people, three blood tests are checked and at least one must be positive and confirmed twice at least three months apart. Some people with these autoantibodies never develop blood clots. Risk factors for developing blood clots include high blood pressure, obesity, smoking, atherosclerosis, birth control pills, or having an associated autoimmune disease like SLE.

What Are Common Treatments?

APS increases the risk of blood clots, so treatment focuses on preventing clot-related complications. In acute events, initial management involves intravenous or subcutaneous (under the skin) injection of blood thinners, followed by long-term oral anticoagulants such as warfarin to reduce the risk of future clots. Additional therapies, including aspirin, hydroxychloroquine, direct oral anticoagulants (DOACs), and immunomodulatory agents, may be considered based on individual needs. For pregnant women with APS, low molecular weight heparin with or without low-dose aspirin may be recommended to help prevent miscarriage. Additionally, those with aPL autoantibodies who have never experienced thrombotic events or miscarriages might also receive preventive therapy, but this should be carefully discussed with a rheumatologist and OB-GYN.

Living with APS

Individuals who take blood thinners long term must see their healthcare provider regularly to monitor the drug. Lifestyle changes should be implemented to prevent blood clots such as managing weight and stop smoking, avoiding estrogen therapy for birth control or menopausal symptoms unless a physician directs.

Updated February 2025 by Howard Yang, MD, RhMSUS, and reviewed by the American College of Rheumatology Committee on Communications and Marketing.

This information is provided for general education only. Individuals should consult a qualified health care provider for professional medical advice, diagnosis and treatment of a medical or health condition.