Objective This study aimed to evaluate the diagnostic performance of plasma methylated SEPT9 (mSEPT9) gene combined with carcinoembryonic antigen (CEA), carbohydrate antigen 199 (CA199), fecal occult blood test (FOBT), red blood cell distribution width (RDW), and inflammation-related indices from complete blood count (CBC) for colorectal cancer (CRC).

Methods A prospective study was conducted on 188 patients pathologically diagnosed with CRC (CRC group) and 693 control subjects with gastrointestinal symptoms but non-CRC diagnoses (control group) admitted to Hunan Provincial People’s Hospital from January 01, 2024 to December 31, 2024. Data on mSEPT9, CEA, CA199, FOBT, and CBC were collected. Binary logistic regression analysis was used to establish a predictive model for CRC risk factors, and receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic performance of each index.

Results The positive rates of mSEPT9 and FOBT in the CRC group were significantly higher than those in the non-CRC group (P<0.001). The levels of CEA, CA199, RDW-CV, RDW-SD, neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) were significantly higher in the CRC group than in the control group (P<0.001), while the lymphocyte-to-monocyte ratio (LMR) was significantly lower (P<0.001). Univariate logistic regression analysis showed that mSEPT9, CEA, CA199, FOBT, RDW-CV, RDW-SD, NLR, and PLR were independent predictive risk factors for CRC. Multivariate regression analysis indicated that patients with positive or elevated mSEPT9, CEA, CA199, FOBT, RDW-CV, and PLR were more likely to have CRC. The combined model of mSEPT9, CEA, CA199, FOBT, RDW-CV, and PLR demonstrated an impressive area under the ROC curve (AUC) of 0.939, with a sensitivity of 0.920 and specificity of 0.839, highlighting excellent screening efficacy for CRC.

Conclusion A screening model incorporating mSEPT9, CEA, CA199, FOBT, RDW-CV, and PLR provides valuable insights for CRC diagnosis.

The authors have declared no competing interest.

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This study protocol was approved by the Ethics Committee of the Hunan Provincial People's Hospital.

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