As many as half of all cases of deep vein thrombosis (DVT) develop without clinical symptoms, and only pulmonary embolism (PE) prompts diagnostic tests. A normal D-dimer test result is enough to rule out DVT when, based on clinical presentation, the probability of DVT is no more than moderate. However, if the likelihood of DVT is clinically high, diagnostic imaging studies are indicated. Before treatment is started (or 1 month after discontinuation of anticoagulant therapy), a blood sample should be collected for the analysis of blood clotting factors (thrombophilia screening; see ) if the patient has a positive family history, recurrent or idiopathic (no identified risk factors) thrombosis, massive thrombosis, miscarriage or thrombi affecting both the venous and arterial vessels, or if the patient is young. Treatment aims to prevent PE and post-thrombotic syndrome. All risk factors, or their absence, must be recorded. They determine the duration of the anticoagulant therapy.