eTable 2. Sensitivity and specificity of red flags (6).

	Sensitivity	Specificity
Malignancy
Age ≥ 50 years History of cancer Unintentional weight loss No relief after 4 weeks of treatment	0.77 0.31 0.15 0.31	0.71 0.98 0.94 0.90
No relief with bed rest Persistence for more than one month Age ≥ 50 years or history of cancer or unintentional weight loss or no relief after one month of treatment	> 0.90 0.50 1.00	0.46 0.81 0.60
Spinal osteomyelitis
Intravenous drug abuse, urinary tract infection, or skin infection	0.40	–
Compression fracture
Age ≥ 50 years Age ≥ 70 years	0.84 0.22	0.61 0.96
Trauma	0.30	0.85
Corticosteroid use	0.06	0.99
Ankylosing spondylitis
Age ≤ 35 years Morning stiffness	0.90 0.64–0.95	0.30 0.29–0.59
No improvement of pain in the supine position Improvement of pain and stiffness on movement	0.80 0.69–0.75	0.49 0.45–0.90
Insidious onset	0.53–0.88	0.51–0.76
Duration of symptoms >3 months Four of the above five signs positive	0.71–0.86 0.95	0.09–0.54 0.85
Disc herniation
Sciatica (assumed prevalence* 5%)	0.95	0.88
Cauda equina syndrome
Urinary retention Saddle anesthesia	0.90 0.75	– –
Sphincter dysfunction	0.60–0.80	–

^*artifact