Table 1

Patient characteristics and biomarker reference intervals of healthy subjects

CharacteristicsPatients (n=60)Healthy subjects*p Value
AS19/axial spondyloarthritis28 2954 (90)/60 (100)
HLA-B27 positivity (%)49 (82)
Gender (male/female) (%)48 (80)/12 (20)
Age (years)40 (21–62)
Disease duration (years)12 (0–45)
Baseline methotrexate use (%)32 (53)
Baseline NSAID use (%)47 (78)
Infliximab/etanercept/adalimumab41 (68)/13 (22)/6 (10)
ASDAS3.86 (1.98–6.19)
BASDAI (0–100)55 (30–98)
BASFI (0–100)48 (10–99)
BASMI (0–100)30 (0–80)
Swollen joint count (0–28)0 (0–9)
Peripheral arthritis11 (18)
Elevated CRP45 (75)
Serum CRP (mg/l)16 (1.2–162)8<0.0001
Plasma IL-6 (ng/l)6.5 (1.4–186)1.3 (0.74–3.30)<0.0001
Plasma VEGF (ng/l)64 (10–896)45 (17–109)0.001
Serum YKL-40 (μg/l)50 (20–271)43 (22–95)0.04
Urinary CTX-II (ng/mmol)474 (103–1554)152 (53–270)<0.0001
Serum total aggrecan (µg/l)565 (203–1162)816 (565–1239)<0.0001
Serum MMP-3 (µg/l)23 (4.3–504)16 (7.0–27)<0.0001
Serum COMP (µg/l)1.58 (0.80–2.50)1.60 (1.15–2.00)NS
Serum CTX-I (µg/l)0.33 (0.07–0.98)0.28 (0.10–0.58)NS
Serum total osteocalcin (µg/l)25.4 (11.0–61.0)20.3 (12.0–34.0)NS
  • Patient values are median (ranges) unless otherwise stated. Values of healthy subjects are median (10th–90th percentiles). Mann–Whitney tests were used for comparison between baseline values and healthy subjects. At baseline, ASDAS could not be calculated in four (7%) patients due to missing data.

  • Patients initiated treatment with either infliximab (3 mg/kg (n=30) or 5 mg/kg (n=11) intravenous at baseline, weeks 2 and 6 and then every 6th to 8th week), etanercept (25 mg subcutaneously twice per week or 50 mg weekly) or adalimumab (40 mg subcutaneously every other week). At week 22, BASDAI responders continued therapy while BASDAI non-responders had an increase in dose of the TNFα inhibitor therapy (n=5), changed therapy (n=5), or continued therapy without any changes (n=8) as decided by the treating rheumatologist.

  • * The reference intervals were established in different groups of healthy subjects: IL-6, n=320;30 VEGF, n=306;31 YKL-40, n=245;32 CTX-II, n=113 (internal laboratory data); total aggrecan, n=152; MMP-3, n=333; COMP, n=294 (personal observations); CTX-I, n=158 (internal laboratory data); and total osteocalcin, n=128 (internal laboratory data).

  • AS, ankylosing spondylitis; ASDAS, ankylosing spondylitis disease activity score; BASDAI, Bath ankylosing spondylitis disease activity index; BASFI, Bath ankylosing spondylitis disease functional index; BASMI, Bath ankylosing spondylitis disease metrology index; COMP, cartilage oligomeric matrix protein; CRP, C-reactive protein; CTX-I, C-terminal cross-linking telopeptide of type I collagen; CTX-II, C-terminal crosslinking telopeptide of type II collagen; HLA-B27, human leucocyte antigen B27; IL-6, interleukin 6; MMP-3, matrix metalloproteinase 3; NS, non-significant; NSAID, non-steroidal anti-inflammatory drug; TNFα, tumour necrosis factor alpha; VEGF, vascular endothelial growth factor.