One of my friends has APLS (antiphospholipid antibody syndrome), which can also occur as a secondary symptom of Lupus. All of her blood tests always come back negative due to the way APLS affects coagulation -- unless the bloodwork is cultured for at least two days. So if you have reason to suspect the test results may be incorrect, ask them to re-do the bloodwork as a long-term culture rather than the normal fast screening.