Hi. Is this test = lupus anticoagulant? If so, I *think* it's used in conjunction with OTHER tests, and also that "disease context" is important.
In his lupus hardcover, which is available in most libraries & bookstores, Dr. Daniel Wallace discusses the OTHER tests needed when someone's PTT-la is elevated, such as antiphospholipid antibodies, syphilis (in which a false-positive is meaningful), plus other specialized tests. In people with LUPUS, these findings act together to assess risk of blood clots, need for medication, etc. (Also see the "sticky post" at the top of the thread list on APS.)
But Dr. Wallace ALSO cites OTHER conditions in which people test positive for antiphospholipid antibodies and lupus anticoagulant, such as rheumatoid arthritis, scleroderma, infectious diseases (particularly AIDS), etc.---yet in these diseases, actual clotting complications are apparently quite rare, despite "positive" test results.
Sorry above is such a muddle, but I'm only a (dumb) patient & have only lupus, not APS... In your shoes, I'd do a little reading, write out questions, then insist on talking to your doctor (NOT a front-desk staffer). Alternatively, you could go right to your doctor, and ask him/her to do a tree-style sketch showing test & disease possibilities. Best wishes to you, sincerely, Vee