Red flags Sudden, severe pain Signs of acute limb ischemia (eg, coolness, pallor, pulse deficits, delayed capillary refill) Dyspnea, chest pain, and / or sweating Signs of systemic toxicity (eg, delirium, tachycardia, shock, pallor) Crepitation, tenseness, foul discharge, bullae, necrosis Risk factors for deep venous thrombosis Neurologic deficits Interpretation of findings It can be helpful to categorize patients by acuity of symptoms and then further narrow the differential diagnosis based on presence or absence of findings of Ischemia Inflammation Neurologic abnormalities Sudden, severe pain suggests acute ischemia or acute radiculopathy (eg, due to sudden disc herniation).