<keypoints>
- Red flags screen for four main serious pathologies: **malignancy**, **fracture**, **infection**, and **cauda equina syndrome (CES)**
- CES is the most urgent: key features are saddle anaesthesia, bladder/bowel dysfunction, bilateral leg weakness, and loss of anal tone
- Serious pathology accounts for <1% of low back pain in primary care, but >80% of patients have at least one red flag, so clinical judgement and the overall picture matter
- Progressive neurological deficit in the lower limbs warrants urgent assessment regardless of other features
</keypoints>
Red Flags by Serious Pathology
Cauda Equina Syndrome (urgent/emergency)
The most time-critical diagnosis. Five key features consistently described in the literature:
- Saddle anaesthesia (perineal/perianal numbness)
- Bladder dysfunction (urinary retention, overflow incontinence, loss of desire to void)
- Faecal incontinence or loss of anal sphincter tone
- Bilateral neurogenic sciatica
- Sexual dysfunction
Progressive bilateral lower limb weakness and widespread sensory deficit are also flags. Incomplete CES (reduced urinary sensation, poor stream without retention) still warrants urgent assessment.
Malignancy
- History of cancer (the single most diagnostically accurate red flag for spinal malignancy)
- Age >50 years
- Unexplained weight loss
- Pain at rest or worsening at night
- Failure to improve with treatment
Fracture
- Significant trauma (or minor trauma if >50 years, osteoporosis, or corticosteroid use)
