Diagnostic Imaging and Laboratory/Diagnostic Studies
Choose studies from the exam, not the calendar
Plain films are reasonable when red flags for fracture, instability, infection, or malignancy exist, or after significant trauma; they are not routine for uncomplicated acute low back pain. MRI is indicated for progressive neurologic deficit, suspected cauda equina syndrome, suspected infection or tumor, and persistent radicular symptoms that fail conservative care. CT images bone better; ultrasound is operator dependent.
Laboratory panels
Commonly ordered: CBC, comprehensive metabolic panel, ESR and CRP for inflammation, HbA1c, TSH, vitamin D, urinalysis, and PSA when age-appropriate. Interpret in the clinical context, not in isolation.
Traps
Assuming a finding is the pain generator-disc degeneration, bulges, and facet arthropathy are common in asymptomatic adults. Ordering imaging that cannot change management. Ignoring incidental findings. Forgetting that gadolinium contrast is risky in significant renal impairment and that pacemakers and metal constrain MRI.
Worked example
A 34-year-old with two weeks of acute low back pain, no red flags, and a normal neurologic exam needs education and a treatment plan, not films. A 68-year-old smoker with night pain, fever, and injection drug use needs urgent labs and imaging the same day. The difference is the pretest probability created by the history.