Factors and conditions that can cause troublesome blood clots, as well as serious conditions that are associated with blood clots, include: Antiphospholipid syndrome. Arteriosclerosis / atherosclerosis. Certain medications, such as oral contraceptives and hormone therapy drugs. Deep vein thrombosis (DVT) Factor V Blood clots · Blood clots Causes - Mayo Clinic · When to see a doctor. Aug 3, - Symptoms of blood clots in specific body locations inclulde: Symptoms of blood clots in legs (deep vein thrombosis, or DVT) are pain, redness, and swelling. Symptoms of an arterial blood clot in a limb (leg or arm) include pain, pale color, numbness, loss of feeling, and coolness to the touch.