The diagnosis of antiphospholipid syndrome is made by testing the blood of patients with blood clots and/or recurrent miscarriages for the presence of anti-phospholipid autoantibodies (aPL). Screening is done using three kinds of tests. Tests may vary because of the differences in the aPL from patient to patient. Each single test cannot detect all of the possible autoantibodies, so their combined use is strongly advised. At least one of these tests must prove positive, and be confirmed on two occasions no less than three months apart. In general, the higher the level of the test and the greater number of positive tests increases the risk of developing symptoms. Having positive blood tests alone in the absence of a clot does not make a diagnosis of antiphospholipid syndrome. There are healthy people who carry these clotting proteins in their blood who never have a clot in their lifetimes.
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