Antiphospholipid antibody syndrome (APS) is a condition defined by the presence of abnormal antibodies and a tendency to form blood clots or to have miscarriages.
People with antiphospholipid antibody syndrome produce antibodies that interact with certain proteins in the blood. This causes the blood to clot more than normal. The most commonly measured antiphospholipid antibodies include lupus anticoagulant and antibodies to cardiolipin or beta-2 glycoprotein.
The blood clots often form in the leg veins. The clots also can form in arteries. The blood clots may occur in any organ, but they tend to favor the lungs, brain, kidneys, heart and skin.
There are two types of APS: primary and secondary. People with primary APS do not have any associated condition. The secondary form is associated with another immune disorder, such as lupus, an infection or, rarely, the use of a medication (such as chlorpromazine or procainamide).
A person may have a blood test that detects antiphospholipid antibodies. This does not necessarily mean that he or she has APS or will develop symptoms or problems of APS.