Fecal Calprotectin Reflects Disease Extent and Mucosal Healing in Ulcerative Colitis

Yes, fecal calprotectin (FC) reflects both disease extent and mucosal healing in ulcerative colitis (UC), as demonstrated by the findings of the prospective observational study mentioned in the context. Here's a detailed explanation based on the study:

### Key Findings:

1. **FC as a Marker of Mucosal Inflammation:**

• FC levels were found to correlate strongly with mucosal inflammation in UC patients. Higher FC concentrations were consistently associated with active inflammation, as assessed both endoscopically (using the Mayo Endoscopic Score, MES) and histologically (using the Nancy Histological Index, NHI).
• This confirms FC as a robust and reliable biomarker for detecting mucosal inflammatory activity.

2. **Impact of Disease Extent on FC Levels:**

• The study revealed that FC levels are influenced by the extent of UC, which is classified according to the Montreal classification into proctitis (limited to the rectum), left-sided colitis (involving up to the splenic flexure), and pancolitis (extending to the entire colon).
• FC concentrations were progressively higher as disease extent increased, even in patients in remission. Patients with pancolitis had the highest FC levels, followed by those with left-sided colitis and proctitis.

3. **FC and Mucosal Healing Across Disease Extent:**

• Despite the influence of disease extent on FC levels, the biomarker maintained high diagnostic accuracy for identifying mucosal healing across all disease extent categories. The area under the receiver-operating characteristic curve (AUROC) for FC ranged from 0.878 to 0.915, indicating excellent performance in detecting mucosal healing.
• No statistically significant differences in diagnostic accuracy were observed between the different disease extent groups, highlighting FC's reliability regardless of whether the disease is limited or extensive.

4. **Primary vs. Secondary Determinants of FC Levels:**

• The study concluded that inflammatory activity is the primary determinant of FC levels, while disease extent has a secondary effect. This means FC is mainly driven by the degree of mucosal inflammation, but disease extent also contributes to the observed FC values.

### Clinical Utility of FC:

• FC serves as a noninvasive, reliable biomarker for monitoring mucosal healing in UC patients, which is critical for assessing disease activity and guiding treatment decisions.
• It is effective across all disease extents, including limited forms such as proctitis, making it a valuable tool for clinicians managing UC patients.

### Conclusion:

Fecal calprotectin reflects both the extent of disease and mucosal healing in ulcerative colitis. It is primarily influenced by inflammatory activity but also shows secondary variation based on disease extent. Importantly, FC remains highly accurate in diagnosing mucosal healing, regardless of the disease's extent, supporting its use as a noninvasive biomarker in clinical practice.