Table 2 Sensitivity and specificity of candidate classification criteria for axial SpA (set 1 and set 2) in patients with chronic back pain of unknown origin and age at onset 45 years or less; n = 649 patients (n = 391 axial SpA, n = 258 no SpA)

Criteria for SpA	Sensitivity (%)	Specificity (%)
Candidate criteria set 1 (IBP experts; ⩾4 of 5)*	87.7	74.0
Candidate criteria set 1 (IBP Calin; ⩾4 of 5)†	89.3	69.4
Candidate criteria set 1 (IBP Berlin; ⩾2 of 4)‡	86.2	76.0
Candidate criteria set 2 (IBP experts; ⩾4 of 5)*	85.7	76.7
ESSG	72.4	66.3
Modified ESSG (with MRI)§	85.1	65.1
Amor	69.3	77.9
Modified Amor (with MRI)¶	82.9	77.5

*Inflammatory back pain (IBP) according to experts;14 at least four of five parameters present. †IBP according to Calin et al;12 at least four of five parameters present. ‡IBP according to Rudwaleit et al;13 at least two of four parameters present. §The European Spondylarthropathy Study Group (ESSG) criteria were modified in that active sacroiliitis on magnetic resonance imaging (MRI) was added to the list of parameters required in addition to inflammatory back pain or synovitis. ¶The Amor criteria were modified in that active sacroiliitis on MRI was assigned 3 scoring points, similar to definite radiographic sacroiliitis. The presence of either definite radiographic sacroiliitis or active sacroiliitis on MRI thus yielded 3 points (maximum of 3 points for the imaging criterion). SpA, spondyloarthritis.