PROS1 and AIDS: Deep vein thrombosis (DVT) is 10 times more common in HIV and AIDS patients, particularly in those with severe immune suppression (CD4 < 200 cells/mL).1,2,3 Opportunistic infections increase the risk of HIV and AIDS patients having a thromboembolic event by lowering protein S levels and through immobility.4,5 Such chronic inflammation in patients with HIV can elevate C4b-binding protein, which binds protein S and decreases free levels.6 Patients seen with DVT are also more likely to be HIV-positive.7