The following information may help to address your question:
There are no definitive facts about the number of people with antiphospholipid (aPL)
About 50% of people with APS have primary APS, which is when their APS is not associated with another disease. Secondary APS is when the APS occurs with systemic lupus erythematosus (SLE) or another autoimmune disorder. Studies show that between 5-30 percent of individuals with blood clots, and no history of SLE, have aPL antibodies. In people with SLE, approximately 30 percent have aPL antibodies, and around 30-50 percent of these individuals have symptoms and signs of APS. Additional studies suggest that aPL antibodies may play a role in about one-third of strokes in people under the age of 50.