**Background:** Crohn's disease (CD) is a chronic inflammatory bowel disease, and approximately 80% of patients require surgery during their lifetime. Postoperative complications occur in 20–40% of CD patients undergoing bowel resection. Preoperative nutritional and immunologic status are recognized as important factors influencing surgical outcomes. The Prognostic Nutritional Index (PNI), calculated from serum albumin and total lymphocyte count, has been validated as a prognostic marker in various malignancies and recently in benign diseases such as ulcerative colitis, but limited evidence exists for its role in CD surgery. This study aimed to investigate whether PNI predicts postoperative complications in CD patients and to develop a predictive nomogram.
**Methods:** This retrospective study enrolled 124 patients who underwent first-time CD-related bowel surgery at the Department of Gastrointestinal Surgery, Ruijin Hospital, from January 2013 to October 2019. Exclusion criteria included unavailable CT data, severe comorbidity, malignancy, HIV infection, prior abdominal surgery, and perianal surgery. PNI was calculated as 10 × albumin (g/dL) + 0.005 × total lymphocyte count (per mL). The optimal PNI cutoff (33.9) was determined by ROC analysis. Patients were divided into low-PNI (≤34, n=39) and high-PNI (>34, n=85) groups. Clinical features, laboratory parameters, and postoperative complications were compared. LASSO logistic regression was used for feature selection, and a nomogram was constructed. Model performance was assessed using the C-index, ROC curve, bootstrapping validation (1000 resamples), and decision curve analysis.
**Key Results:** The cohort was 59.7% male, mean age 37.06 ± 13.08 years, mean disease duration 55.81 ± 51.67 months. The median PNI was 37.2 (range 15.3–55.5). Low-PNI patients had significantly lower serum albumin (23.4 ± 4.8 vs 35.8 ± 5.2 g/L, p<0.001), hemoglobin (98.0 ± 24.1 vs 115.8 ± 22.2 g/L, p<0.001), and higher WBC counts (8.3 ± 5.4 vs 6.3 ± 3.0 ×10^9/L, p=0.009). Overall postoperative complications occurred in 35 of 124 patients (28.2%): 20 of 39 (51.3%) in the low-PNI group vs 15 of 85 (17.6%) in the high-PNI group (p<0.001). Low-PNI patients had significantly longer postoperative hospital stays (23.46 ± 23.85 vs 13.13 ± 13.00 days, p=0.002). LASSO regression selected 7 predictors: sex, BMI, myopenia, age, surgical indication, PNI, and HBI score. The nomogram demonstrated a C-index of 0.824 (95% CI 0.750–0.898), confirmed as 0.701 by bootstrapping. The AUC was 0.824. Decision curve analysis showed clinical utility at threshold probabilities between 2% and 74%. High-risk patients (nomogram score >273) had significantly longer postoperative stays than low-risk patients (17.07 ± 24.73 vs 10.36 ± 4.51 days, p=0.02).
**Clinical Implications:** This study demonstrates that preoperative PNI is significantly associated with postoperative complications in CD patients undergoing bowel surgery, with a low PNI (≤34) identifying a high-risk group. The PNI cutoff of 33.9 is lower than reported for colorectal cancer (45) or ulcerative colitis (47), likely reflecting the generally poorer nutritional status of CD patients. The nomogram integrating PNI with other clinical factors (sex, BMI, myopenia, age, indication, HBI) provides a practical tool for preoperative risk stratification. Limitations include the retrospective design, small sample size (n=124), potential confounding from albumin supplementation and preoperative steroids/immunosuppressants, and lack of external validation. Future studies with larger, independent cohorts are needed to validate and refine the nomogram.