Reference Candidate biomarker Sampling Population Findings Notes Hoffman et al. [41 ] ASCA (IgA and/or IgG) Serum 26 patients with CD, 108 patients with SpA, 56 patients with RA, and 45 healthy controls ASCA IgA levels similar between patients with SpA with and without histologically proved gut inflammation ASCA IgA levels were raised in AS and uSpA vs. RA and HC (AUC 0.72) Bernardi et al. [80 ] YKL-40 Serum 171 patients: 29 PsA, 66 IBD (36 CD and 30 UC), and 76 SpA/IBD (44 CD/32 UC) YKL-40 levels significantly higher in SpA/IBD vs. IBD patients (AUC 0.82) De Vries et al. [48 ] pANCA Serum 179 patients: 52 with AS, 50 with UC, 51 with CD, and 26 with IBD+AS pANCA associated with UC in AS patients (OR 8.2, 95% CI 1.2–55.6) pANCA detected in 21% of AS patients ASCA (IgA and/or IgG) Serum 179 patients: 52 with AS, 50 with UC, 51 with CD, and 26 with IBD+AS ASCA found in 40% of SpA/CD vs. 30% of AS and 90% of CD patients Not useful OmpC antibodies Serum 179 patients: 52 with AS, 50 with UC, 51 with CD, and 26 with IBD+AS OmpC Ab found in 30% of SpA/IBD patients and 19% of AS patients Not useful Al-Jarallah et al. [81 ] Anti-MCV Serum 125 IBD patients (44 of which with SpA/IBD) vs. 81 healthy controls Anti-MCV positivity similar between IBD and HC (16.8% vs. 16.0%) Not useful Anti-CCP2 Serum 125 IBD patients (44 of which with SpA/IBD) vs. 81 healthy controls Anti-CCP2 positivity similar between IBD and HC (6.4% vs. 6.2%) Not useful Wallis et al. [49 ] ASCA IgG and IgA Serum 76 patients with AS, 77 patients with AS/IBD, and 48 patients with mechanical back pain ASCA IgG higher in AS/IBD than AS patients (14% vs. 0%) Anti-OmpC Serum 76 patients with AS, 77 patients with AS/IBD, and 48 patients with mechanical back pain Anti-OmpC higher in AS/IBD than AS patients (27% vs. 12%) Anti-CBir1 Serum 76 patients with AS, 77 patients with AS/IBD, and 48 patients with mechanical back pain Anti-CBir1 higher in AS/IBD than AS patients (42% vs. 20%) ANCA Serum 76 patients with AS, 77 patients with AS/IBD, and 48 patients with mechanical back pain ANCA not significantly different between AS/IBD and AS patients Not useful Klingberg et al. [55 ] Calprotectin Feces 164 AS patients followed up for 5 years The development of CD (3 pts) predicted by Fecal calprotectin was elevated (>50 mg/kg) in 70% pts at the baseline Viladomiu et al. [88 ] IgA-coated E. coli Fecal microbiome 59 IBD patients with or without peripheral SpA IgA-coated E. coli enriched in CD-SpA vs. CD alone CD-SpA E. coli isolates induced Th17 mucosal immunity Luchetti et al. [74 ] SOST Serum 85 pts with axial or peripheral SpA/IBD Lower levels in AxSpA/IBD vs. PerSpA/IBD and control groups (AUC 0.88) Lower levels of SOST correlate with higher levels of anti-SOST-Ig Anti-SOST antibodies Serum 85 pts with axial or peripheral SpA/IBD Higher levels in AxSpA/IBD vs. PerSpA/IBD and control groups (AUC 0.84) Higher levels of anti-SOST-Ig correlate with lower levels of SOST
