Red flag symptoms in back pain — seek urgent medical attention:
- Saddle anaesthesia (numbness around buttocks, groin, inner thighs) + bladder/bowel dysfunction (cauda equina syndrome — surgical emergency)
- Back pain with unexplained weight loss, night sweats or fever (cancer or infection)
- Back pain in someone over 50 with a history of cancer
- Back pain following significant trauma
- Progressive neurological weakness in legs
Blood tests ordered for back pain investigation
| Test | What it checks for | Significant result |
|---|---|---|
| ESR | Very high ESR suggests infection (discitis, osteomyelitis) or malignancy | >50 mm/hr is significant |
| CRP | Active inflammation; rises rapidly with infection | >50 mg/L in spinal infection |
| CBC | Anaemia (malignancy, chronic disease); infection (raised WBC) | Depends on cause |
| ALP (alkaline phosphatase) | Bone metastases, Paget disease of bone | Elevated |
| Calcium | Bone metastases, myeloma causing hypercalcaemia | >10.5 mg/dL |
| PSA (prostate specific antigen) | Prostate cancer metastases to spine | Elevated in men with bone pain |
| Serum protein electrophoresis (SPEP) | Multiple myeloma (plasma cell cancer causing lytic bone lesions) | Paraprotein band |
| HLA-B27 gene test | Ankylosing spondylitis (inflammatory back pain) | Positive in ~90% of AS |
| Uric acid | Gout affecting the spine (rare) | >7.2 mg/dL (men) |
Types of back pain
Mechanical back pain (most common — ~85%)
Localised lower back pain worsened by movement and eased with rest. Often from muscle strain, disc degeneration or facet joint arthritis. No neurological features. Blood tests normal. X-rays and MRI often show degenerative changes but may not be clinically relevant. Treated with physiotherapy, NSAIDs and remaining active (bed rest prolongs recovery).
Radiculopathy (sciatica)
Pain radiating from the lower back into the leg, following a nerve distribution (dermatomal). L4-S1 disc prolapse compresses sciatic nerve roots, causing buttock and leg pain, with numbness, tingling and weakness. Blood tests normal. MRI confirms disc herniation. Most resolve within 6–12 weeks with physiotherapy; severe cases may need nerve root injection or surgery.
Ankylosing spondylitis (inflammatory back pain)
Chronic inflammatory arthritis of the spine and sacroiliac joints. Classic features: onset before age 40, insidious onset, morning stiffness lasting over 1 hour, improves with exercise (unlike mechanical back pain which worsens), may also affect eyes (uveitis) and gut. ESR and CRP elevated in active disease. HLA-B27 positive in ~90%. X-ray shows sacroiliitis and bamboo spine in advanced disease. MRI detects earlier changes. Treated with NSAIDs and biologics (TNF inhibitors).
Spinal infection (discitis / osteomyelitis)
Bacterial infection of the disc or vertebra, most commonly caused by Staphylococcus aureus. Severe constant back pain, worse at rest, with fever. ESR and CRP dramatically elevated. Blood cultures may be positive. MRI is the imaging of choice. Treated with prolonged IV antibiotics.
Questions to ask your doctor
- Are there any red flag symptoms that need urgent investigation?
- Should I have an MRI of my spine?
- Could this be inflammatory back pain (ankylosing spondylitis)?
- Do I need a PSA or protein electrophoresis to exclude cancer?
- Is physiotherapy appropriate for my type of back pain?