What is the first diagnostic test to order for a patient with back pain?

First Diagnostic Test for Back Pain

For uncomplicated back pain without red flags, no imaging is needed initially—clinical assessment and conservative management should be pursued for 4-6 weeks before considering any diagnostic testing. However, the appropriate first test depends critically on the presence or absence of red flags and neurological symptoms.

Clinical Decision Algorithm

Patients WITHOUT Red Flags or Neurological Deficits

• No imaging is indicated for the first 4-6 weeks of acute low back pain 1, 2, 3
• The natural history of nonspecific low back pain is favorable with spontaneous improvement over time 2
• Imaging findings correlate poorly with symptoms in uncomplicated cases and do not change management 2, 3
• Maintain activity levels and pursue conservative treatment during this initial period 4, 3

Patients WITH Red Flags BUT NO Neurological Deficits

• Plain radiographs (AP and lateral views) are the standard first-line imaging test 5
• Radiographs provide 9-22% diagnostic yield when combined with detailed history and physical examination 5
• Lateral view is more sensitive than AP view and may be sufficient for initial screening 6
• Oblique views add minimal diagnostic information and should not be routinely ordered 5

Patients WITH Neurological Deficits (Motor Weakness, Saddle Anesthesia, Bowel/Bladder Dysfunction)

• Urgent MRI of the lumbar spine without contrast is the first-line test 7, 8
• This represents a medical urgency—do NOT delay imaging for a trial of conservative therapy 8
• MRI provides superior soft tissue visualization of vertebral marrow, spinal canal, nerve roots, and intervertebral discs 7, 8
• CT may substitute if MRI is unavailable, though it is inferior for soft tissue evaluation 8
• Delayed diagnosis of neurologic deficits leads to poorer outcomes and potential permanent disability 7, 8

Critical Red Flags Requiring Imaging

Red flags that warrant immediate imaging include: 5, 3

• Morning stiffness
• Gait abnormalities
• Night pain
• Neurologic deficit (motor weakness, sensory loss, reflex changes)
• Radiating pain with progressive symptoms
• Fever (suggesting infection)
• Unintentional weight loss (suggesting malignancy)
• Pain lasting >4 weeks without improvement
• History of cancer (particularly breast, lung, prostate, kidney, thyroid)
• Tachycardia or lymphadenopathy
• Abnormal spinal curvature

Common Pitfalls to Avoid

Do NOT order plain radiographs when neurological deficits are present

• Plain films cannot visualize discs, nerve roots, or spinal canal adequately 8
• This delays appropriate diagnosis and risks permanent neurological damage 7, 8

Do NOT routinely image uncomplicated acute low back pain

• Imaging in the absence of red flags leads to unnecessary radiation exposure, cost, and potential cascade of interventions without improving outcomes 1, 2, 3
• Reassess clinically at 4-6 weeks if symptoms persist 2, 4

Do NOT skip directly to advanced imaging without clinical justification

• When red flags are present but neurological examination is normal, plain radiographs should be obtained first 5
• Negative radiographs do not exclude pathology but guide the need for advanced imaging 5

When to Escalate Beyond Initial Imaging

After negative plain radiographs in patients with persistent red flags: 5

• MRI without contrast increases diagnostic yield by 25-34% 5
• Bone scan with SPECT/CT is appropriate when bony pathology (spondylolysis, osseous neoplasm) is suspected 5
• CT without contrast may be useful for evaluating nondisplaced fractures or spondylolysis 5

Contrast administration is reserved for specific scenarios: 5, 8

• Suspected neoplasm
• Suspected discitis/osteomyelitis
• Postoperative evaluation
• Precontrast images should always be obtained first to accurately assess enhancement 5