Oncostatin M as a Complementary Non-Invasive Marker of Endoscopic and Histological Disease Activity in Ulcerative Colitis

Plasma Oncostatin M (OSM) has been proposed as a biomarker of disease activity in ulcerative colitis (UC). We evaluated OSM’s relationship with clinical, endoscopic, and histological activity across two follow-up visits, compared with fecal calprotectin (FC). One hundred UC patients were assessed at Visit 1 (baseline) and Visit 2 (12 months) for clinical (partial Mayo score), endoscopic (Mayo Endoscopic Score), and histological (Nancy Histological Index) activity, alongside plasma OSM, FC, CRP, and fibrinogen; 30 healthy controls were included for comparison. Given the marked right-skewness of OSM and FC, associations were assessed using both Pearson and Spearman correlations, and logistic regression effect sizes are reported as odds ratios per doubling of biomarker concentration (log2 scale). OSM correlated significantly with all activity measures at both visits, most strongly with histological activity (r = 0.521–0.602), but weakly or not with CRP/fibrinogen. OSM was significantly elevated versus controls at both visits (p < 0.001) and declined significantly with treatment response (Δ = −89.06 vs. +0.50 in controls, p = 0.006). FC was the dominant predictor of clinical (AUC = 0.788) and endoscopic (AUC = 0.926) remission at Visit 2, with OSM contributing little independent value; however, for histological remission, both baseline OSM and ΔOSM were independent, complementary correlates (OR = 8.43 and 9.64 per doubling, respectively; p < 0.001 for both), yielding the strongest model overall (AUC = 0.949). OSM’s discriminative accuracy improved markedly from Visit 1 to Visit 2 for endoscopic (AUC 0.695 → 0.897) and histological (AUC 0.738 → 0.927) activity. Across two follow-up assessments, OSM consistently reflected UC activity, with its strongest and most independent signal for histological inflammation, both as a concurrent correlate and—more modestly—as a genuine prospective marker independent of baseline treatment exposure. OSM’s incremental value over FC was most apparent for histological status and for stringent (MES 0) endoscopic remission, but not for conventional clinical or endoscopic remission thresholds.