The clinician evaluates acute low back pain using an evidence-based algorithm that identifies red flags warranting urgent investigation while avoiding unnecessary imaging for mechanical/non-specific low back pain (which accounts for 85-90% of cases). Red flags requiring urgent imaging and/or referral include: cauda equina syndrome (bilateral leg weakness, saddle anesthesia, urinary retention or incontinence, fecal incontinence -- requires emergent MRI and surgical consultation), progressive neurological deficit, suspected spinal infection (fever, IV drug use, recent bacteremia, immunosuppression, point tenderness over vertebral body), suspected malignancy (history of cancer, unexplained weight loss, age greater than 50 with new-onset back pain, pain worse at night not relieved by position change), suspected vertebral compression fracture (osteoporosis risk factors, corticosteroid use, age greater than 70, significant trauma, point tenderness over spinous process), and abdominal aortic aneurysm (age greater than 60, pulsatile abdominal mass, vascular disease risk factors). In the absence of red flags, imaging is NOT recommended in the first 4-6 weeks of acute low back pain per all major guidelines (Canadian, ACP, ACR). The clinician prescribes evidence-based first-line treatment: patient education and reassurance (favorable natural history...