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Table 4 Clinical characteristics and HLA-B27 test results of patients with nonradiographic axial spondyloarthritis, ankylosing spondylitis, and other inflammatory back pain

From: The prevalence and clinical characteristics of nonradiographic axial spondyloarthritis among patients with inflammatory back pain in rheumatology practices: a multinational, multicenter study

  Total (N = 914) nr-axSpA (n = 266) AS (n = 491) Other IBP (n = 157) p Value
HLA-B27 test results (when available)      <0.001
 Positive, n (%) 397 (72.98 %) 135 (71.43 %) 250 (82.78 %) 12 (22.64 %)  
 Negative, n (%) 147 (27.02 %) 54 (28.57 %) 52 (17.22 %) 41 (77.36 %)  
Years from IBP to SpA diagnosis      0.747
 Number of patients 179 98 27 54  
 Mean ± SD, years 5.40 ± 7.98 5.21 ± 7.69 6.48 ± 8.53 5.19 ± 8.32  
Family history of SpA      <0.001
 Yes, n (%) 220 (24.07 %) 70 (26.32 %) 132 (26.88 %) 18 (11.46 %)  
 No, n (%) 650 (71.12 %) 180 (67.67 %) 343 (69.86 %) 127 (80.89 %)  
 Results not available, n (%) 44 (4.81 %) 16 (6.02 %) 16 (3.26 %) 12 (7.64 %)  
Family history of SpA (excluding missing)      <0.001
 Yes, n (%) 220 (25.29 %) 70 (28.00 %) 132 (27.79 %) 18 (12.41 %)  
 No, n (%) 650 (74.71 %) 180 (72.00 %) 343 (72.21 %) 127 (87.59 %)  
NSAID response      0.125
 Positive, n (%) 657 (71.88 %) 183 (68.80 %) 358 (72.91 %) 116 (73.89 %)  
 Negative, n (%) 231 (25.27 %) 72 (27.07 %) 125 (25.46 %) 34 (21.66 %)  
 Results not available, n (%) 26 (2.84 %) 11 (4.14 %) 8 (1.63 %) 7 (4.46 %)  
Most recent CRP value      0.146
 Number of patients 767 226 421 120  
 Mean ± SD, mg/L 16.7 ± 26.0 15.8 ± 28.2 18.2 ± 25.3 13.2 ± 23.5  
Most recent CRP level      <0.001
 Not elevated (<3.5 mg/L), n (%) 219 (23.96 %) 72 (27.07 %) 96 (19.55 %) 51 (32.48 %)  
 Elevated (≥3.5 mg/L), n (%) 548 (59.96 %) 154 (57.89 %) 325 (66.19 %) 69 (43.95 %)  
 Results not available, n (%) 147 (16.08 %) 40 (15.04 %) 70 (14.26 %) 37 (23.57 %)  
Most recent CRP level (excluding missing)      <0.001
 Not elevated (<3.5 mg/L), n (%) 219 (28.55 %) 72 (31.86 %) 96 (22.80 %) 51 (42.50 %)  
 Elevated (≥3.5 mg/L), n (%) 548 (71.45 %) 154 (68.14 %) 325 (77.20 %) 69 (57.50 %)  
Most recent ESR value      0.009
 Number of patients 846 252 464 130  
 Mean ± SD, mm/h 29.0 ± 23.6 26.8 ± 23.9 31.2 ± 23.6 25.3 ± 22.8  
Most recent ESR level      <0.001
 Not elevated (<28 mm/h), n (%) 482 (52.74 %) 158 (59.40 %) 237 (48.27 %) 87 (55.41 %)  
 Elevated (≥28 mm/h), n (%) 364 (39.82 %) 94 (35.34 %) 227 (46.23 %) 43 (27.39 %)  
 Results not available, n (%) 68 (7.44 %) 14 (5.26 %) 27 (5.50 %) 27 (17.20 %)  
Most recent ESR level (excluding missing)      <0.001
 Not elevated (<28 mm/h), n (%) 482 (56.97 %) 158 (62.70 %) 237 (51.08 %) 87 (66.92 %)  
 Elevated (≥28 mm/h), n (%) 364 (43.03 %) 94 (37.30 %) 227 (48.92 %) 43 (33.08 %)  
  1. Abbreviations: AS ankylosing spondylitis, CRP C-reactive protein, ESR erythrocyte sedimentation rate, HLA-B27 human leukocyte antigen B27, IBP inflammatory back pain, nr-axSpA nonradiographic axial spondyloarthritis, NSAID nonsteroidal anti-inflammatory drug, SpA spondyloarthritis
  2. The p values represent the omnibus statistical comparison of percentages (or means) across IBP groups based on the chi-square values