Plasma Calprotectin and Myeloperoxidase as Biomarkers in Inflammatory Bowel Disease.

Background: Inflammatory bowel disease (IBD) is a relapsing-remitting illness requiring proactive monitoring of gut inflammation. We aimed to determine the correlations of plasma myeloperoxidase (pMPO) and calprotectin (pCal), two neutrophil proteins, with existing measures of disease activity.

Methods: Adults with IBD undergoing ileocolonoscopy were recruited prospectively. Baseline assessments included blood tests (pMPO, pCal, and C-reactive protein ([CRP]), symptom questionnaires, and endoscopic indices (simple endoscopic score for CD [SES-CD] and UC endoscopic index of severity [UCEIS]). Active IBD was defined as SES-CD > 2 and UCEIS ≥ 2. Spearman's rank correlations assessed the associations between blood markers and endoscopic activity. The area under the receiver operating characteristics curves (AUROC) and univariable logistic regression assessed the ability of blood markers (at optimal thresholds) to identify active disease.

Results: In total, 170 participants were included (female, n = 92; Crohn's disease [CD], n = 99; median age 46 years, IQR 35-58). Plasma biomarkers more accurately identified active IBD in individuals with UC (AUROCpMPO = 0.76, P < .001; AUROCpCal = 0.66, P < .05; AUROCCRP = 0.73, P < .001) than in CD (AUROCpMPO = 0.62, P > .05; AUROCpCal = 0.65, P < .01; AUROCCRP = 0.66, P < .01). In all patients with IBD, the addition of pCal (AUROC = 0.73, P < .001) and pMPO (AUROC = 0.73, P < .001) to CRP added benefit compared to CRP (AUROC = 0.70, P < .001) alone. Plasma myeloperoxidase > 13.86 ng/mL (odds ratio [OR] = 10.13, 3.4-30.16) and pCal > 961.72 ng/mL (OR = 3.38, 1.21-9.4) were associated with an increased odds of having endoscopically active UC.

Conclusions: Plasma MPO shows promise as a potential blood-based biomarker of IBD activity, especially in UC. The combined use of pMPO and CRP adds diagnostic utility in discriminating between active versus quiescent IBD.