To investigate the correlation between the imaging features of small bowel CT enterography (CTE) and the levels of serum systemic immune-inflammation index (SII) and fecal calprotectin (FC) in patients with Crohn's disease (CD), and to analyze the diagnostic efficacy of single and combined detection of CTE, SII and FC for disease activity.

A retrospective study was conducted. A total of 208 patients with CD who visited the Department of Gastroenterology and Department of Radiology, Zhangjiagang Hospital Affiliated to Soochow University between January 2023 and May 2026 were enrolled as research subjects. Clinical data of the patients were retrieved from the hospital's electronic medical record system and picture archiving and communication system. All enrolled patients underwent small bowel CTE, blood routine tests related to SII and quantitative FC detection simultaneously. Two radiologists with more than 10 years of experience in abdominal imaging diagnosis independently completed the evaluation of CTE imaging features by a blind method, and the patients were grouped accordingly. The Simple Endoscopic Score for CD (SES-CD) was used as the gold standard for the judgment of disease activity. Point-biserial correlation and Spearman rank correlation were used to analyze the correlation between CTE imaging features and serum SII and FC, and receiver operating characteristic (ROC) curve was used to evaluate the diagnostic efficacy of single and combined detection of each index for disease activity.

Patients with positive CTE imaging features including stratified enhancement, comb sign, bowel wall ulceration, intestinal stenosis, mesenteric fibrofatty proliferation, and mesenteric lymphadenopathy had significantly higher serum SII and FC levels than those without the corresponding imaging features (P<0.001). The thicker the bowel wall and the higher the ΔCT value of the bowel wall, the higher the serum SII and FC levels of the patients, with statistically significant differences between groups (P<0.001). Spearman rank correlation analysis showed that all included CTE imaging features were significantly positively correlated with serum SII and FC (P<0.001), among which bowel wall thickness had the strongest correlation with FC (r=0.785). ROC curve analysis showed that the combined model constructed by binary Logistic regression of CTE, serum SII and FC had the highest area under the curve (AUC) of 0.884 for diagnosing CD activity, with a sensitivity of 90.57% and a specificity of 79.63%, which was significantly higher than that of each single index (P<0.05). Among the single indexes, FC had the best diagnostic efficacy (AUC=0.796), followed by the comprehensive CTE imaging score (AUC=0.785), and serum SII also had good diagnostic value (AUC=0.742). The diagnostic efficacy of each single index was statistically significant (P<0.001).

There exists a significant positive correlation between the small intestinal CTE features of patients with CD and their serum SII and FC levels. CTE, serum SII and FC can all effectively evaluate the disease activity of CD. Combined detection of the three indicators can significantly improve the diagnostic efficacy for CD disease activity, and provide a reliable basis for non-invasive and accurate assessment of CD conditions in clinical practice.