Most back pain is not caused by anything dangerous. A small fraction is, and the purpose of red flags is to find that fraction without over-investigating everyone else.
New difficulty passing urine or loss of bladder or bowel control · numbness around the genitals, buttocks or inner thighs · weakness in both legs. These may indicate cauda equina syndrome, where delay causes permanent harm.
The four categories
Guidelines between them list 46 discrete red flags, clustering into four serious pathologies:1
| Category | Features most often listed |
|---|---|
| Fracture | Significant trauma; long-term corticosteroid or immunosuppressant use; older age; osteoporosis |
| Malignancy | History of cancer; unexplained weight loss; pain that is unrelieved by rest or worse at night |
| Infection | Fever; intravenous drug use; recent spinal procedure; immunosuppression |
| Cauda equina | Saddle numbness; urinary retention or incontinence; faecal incontinence; bilateral leg symptoms |
For fracture, the two flags nearly every guideline agrees on are major trauma and steroid use. For malignancy, history of cancer and unintentional weight loss.1
Why single flags are weak on their own
This is the part usually left out. Individual red flags have poor standalone diagnostic accuracy and produce high rates of false positives. Prediction models combining several flags perform considerably better than any single historical feature.2
For cauda equina specifically, a systematic review comparing red flags with MRI found pooled sensitivity of 0.19–0.43 and specificity of 0.62–0.88.3 Read that carefully: these signs are more specific than sensitive. Their absence does not rule the condition out, but their presence justifies prompt investigation.
What this means in practice
- A single flag in isolation is a reason for clinical judgement, not automatic imaging.
- A combination of flags, or any cauda equina feature, changes the urgency immediately.
- Absence of flags is reassuring for serious pathology, but does not explain the pain — most back pain is non-specific and still real.
Imaging
MRI is the reference standard for cord compression, cauda equina syndrome and spinal epidural haematoma. Outside those situations, early imaging in the absence of red flags changes management little and is associated with worse outcomes — see when imaging is useful.
Related
What the library can and cannot tell you is set out in the disclaimer. For the common, non-serious causes, see does sitting cause back pain? and posture and pain.
Footnotes
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Red flags presented in current low back pain guidelines: a review. 2016. ↩ ↩2
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Finucane LM, et al. International framework for red flags for potential serious spinal pathologies. JOSPT, 2020. ↩
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Diagnostic accuracy of red flags related to cauda equina syndrome compared with MRI: a systematic review. 2018. ↩
General information, not medical advice. Every claim carries its source; where the evidence is thin, the page says so.Editorial policy · How we grade evidence · All sources · Disclaimer