Patient in the ICU for more than 2 calendar days Patients with DVT or PE diagnosed within the last year Patients receiving chronic systemic anticoagulation Patients who have received up to the time of ICU admission or are receiving therapeutic dose of anticoagulation with UFH or LMWH or other anticoagulants  Inability or contraindication to obtain adequate ultrasound on the lower extremities  Burns in the lower extremities, lacerations, active skin infection, & ischemic limb in the legs, large dressings or in the thighs that prevent adequate ultrasounds Acute ischemia in the lower extremities Amputated foot or leg on one or two sides Compartment Syndrome Severe peripheral arterial disease Vein ligation, gangrene, recent vein grafts, and draining incisions Evidence of bone fracture in lower extremities Patients with Inferior Vena Cava (IVC) Filter Known or suspected pregnancy Limitation of life support, life expectancy <7 days or palliative care Previously enrolled in DETECT trial within the last 180 days Enrolled in another trial for which co-enrolment is not approved