Background: Mucosal healing in ulcerative colitis (UC) is reported to be associated with
favourable clinical outcomes such as reduced hospitalization and surgery rates. Activity
monitoring by endoscopy has its shortcomings due to invasiveness, costs, and potential
patient discomfort. Data on the correlation of noninvasive biomarkers with endoscopic
severity in UC are scarce. Aim: to evaluate the correlation between endoscopic activity
according to the modified Baron Index and fecal calprotectin, C-reactive protein (CRP),
blood leukocytes, and the Lichtiger Index (clinical score). Methods: UC patients with leftsided
and extensive colitis undergoing complete colonoscopy were prospectively enrolled
and scored clinically and endoscopically. Fecal and blood samples were analyzed in UC
patients (in a blinded fashion) and controls. The modified Baron score describes the following
5 endoscopic conditions: 0 = normal, 1 = granular mucosa, edema, 2 = friable mucosa but no
spontaneous bleeding, 3 = microulcerations with spontaneous bleeding, 4 = gross ulceration,
denuded mucosa. Results: We enrolled 228 UC patients (mean age 41 ± 13 years, 39 female)
and 52 healthy controls. Disease was located in 40% in the left colon, 21% had an extensive
and 39% a pancolitis. Endoscopic disease activity correlated best with fecal calprotectin
(Spearman's rank correlation coefficient r = 0.821), followed by the Lichtiger Index (r =
0.682), CRP (r = 0.556), and blood leukocytes (r = 0.401). Fecal calprotectin was the only
marker that could discriminate between different grades of endoscopic activity (grade 0, 25
± 11 μg/g; grade 1, 44 ± 34 μg/g; grade 2, 111 ± 74 μg/g; grade 3, 330 ± 332 μg/g; grade
4, 659 ± 319 μg/g; P = 0.002 for discriminating grade 0 vs. 1, and P < 0.001 for discriminating
grade 1 vs. 2, grade 2 vs. 3, and grade 3 vs. 4). Fecal calprotectin had the highest overall
accuracy (91%) to detect endoscopically active disease (modified Baron Index ≥ 2), followed
by the Lichtiger Index score of ≥ 4 (77%), CRP > 5 mg/L (69%) and blood leukocytosis
(58%). Conclusions: Fecal calprotectin better correlated with endoscopic disease activity
than clinical activity, CRP, and blood leukocytes. The strong correlation with endoscopic
disease activity suggests that FC represents a useful biomarker for noninvasive monitoring
of disease activity in UC patients.