BACKGROUND: The accuracy of noninvasive markers for the detection of 
endoscopically active ulcerative colitis (UC) according the Rachmilewitz Score 
is so far unknown. The aim was to evaluate the correlation between endoscopic 
disease activity and fecal calprotectin, Clinical Activity Index, C-reactive 
protein (CRP), and blood leukocytes.
METHODS: UC patients undergoing colonoscopy were prospectively enrolled and 
scored independently according the endoscopic and clinical part of the 
Rachmilewitz Index. Patients and controls provided fecal and blood samples for 
measuring calprotectin, CRP, and leukocytes.
RESULTS: Values in UC patients (n = 134) compared to controls (n = 48): 
calprotectin: 396 ± 351 versus 18.1 ± 5 μg/g, CRP 16 ± 13 versus 3 ± 2 mg/L, 
blood leukocytes 9.9 ± 3.5 versus 5.4 ± 1.9 g/L (all P < 0.001). Endoscopic 
disease activity correlated closest with calprotectin (Spearman's rank 
correlation coefficient r = 0.834), followed by Clinical Activity Index (r = 
0.672), CRP (r = 0.503), and leukocytes (r = 0.461). Calprotectin levels were 
significantly lower in UC patients with inactive disease (endoscopic score 0-3, 
calprotectin 42 ± 38 μg/g), compared to patients with mild (score 4-6, 
calprotectin 210 ± 121 μg/g, P < 0.001), moderate (score 7-9, calprotectin 392 ± 
246 μg/g, P = 0.002), and severe disease (score 10-12, calprotectin 730 ± 291 
μg/g, P < 0.001). The overall accuracy for the detection of endoscopically 
active disease (score ≥4) was 89% for calprotectin, 73% for Clinical Activity 
Index, 62% for elevated CRP, and 60% for leukocytosis.
CONCLUSIONS: Fecal calprotectin correlated closest with endoscopic disease 
activity, followed by Clinical Activity Index, CRP, and blood leukocytes. 
Furthermore, fecal calprotectin was the only marker that reliably discriminated 
inactive from mild, moderate, and highly active disease, which emphasizes its 
usefulness for activity monitoring.