These tests must be carried out on a minimum of two occasions at least 6 weeks apart and be positive on each occasion, demonstrating persistent positivity, to allow a diagnosis of antiphospholipid syndrome. This is to prevent patients with transient positive tests (due to infection etc.) being diagnosed as positive.Distinguishing a lupus antibody from a specific coagulation factor inhibitor (e.g. : factor VIII) is normally achieved by differentiating the effects of a lupus anticoagulant on factor assays from the effects of a specific coagulation factor antibody. The lupus anticoagulant will inhibit all the contact activation pathway factors (factor VIII, factor IX, factor XI and factor XII). Lupus anticoagulant will also rarely cause a factor assay to give a result lower than 35 iu/dl (35%) whereas a specific factor antibody will rarely give a result higher than 10 iu/dl (10%). Monitoring IV anticoagulant therapy by the PTT ratio is compromised due to the effects of the lupus anticoagulant and in these situations is generally best performed using a chromogenic assay based on the inhibition of factor Xa by antithrombin in the presence of heparin. Anticardiolipin antibodies
Anti-cardiolipin antibodies can be detected using an enzyme-linked immunosorbent assay (ELISA) immunological test, which screens for the presence of β2glycoprotein 1 dependent anticardiolipin antibodies. A low platelet count and positivity for antibodies against β2-glycoprotein 1 or phosphatidylserine may also be observed in a positive diagnosis.
In APS patients, the most common venous event is deep vein thrombosis of the lower extremities, and the most common arterial event is stroke. In pregnant person affected by APS, there is an increased risk of recurrent miscarriage, intrauterine growth restriction, and preterm birth. A frequent cause of such complications is placental infarctions. In some cases, APS seems to be the leading cause of intellectual and/or developmental disabilities in the newborn, due to an aPL-induced inhibition of trophoblast differentiation. The antiphospholipid syndrome is responsible for most of the miscarriages in later trimesters seen in concomitant systemic lupus erythematosus and pregnancy.Other common findings, although not part of the APS classification criteria, are low platelet count, heart valve disease, and livedo reticularis. There are also associations between antiphospholipid antibodies and different neurologic manifestations including headache, migraine, epilepsy, and dementia. Some studies have shown the presence of antiphospholipid antibodies in the blood and spinal fluid of patients with psychological symptoms. Cancer is also observed to comorbid in patients with APS. Risk factors
Risk factors for developing antiphospholipid syndrome include:

Genetic Markers: HLA-DR4, HLA-DR7, and HLA-DRw53
Race: Blacks, Hispanics, Asians, and Native Americans

Pathogenesis
Antiphospholipid syndrome is an autoimmune disease, in which "antiphospholipid antibodies" (anticardiolipin antibodies and lupus anticoagulant) react against proteins that bind to anionic phospholipids on plasma membranes. Like many autoimmune diseases, it is more common in women than in men. The exact cause is not known, but activation of the system of coagulation is evident.