The disease emphasizes early diagnosis. For middle-aged and elderly patients (especially those with cancer or intestinal polyps in their families), whenever unexplained bloody stools or changes in defecation habits occur recently, or unexplained iron deficiency anemia, the possibility of this disease should be considered first, and various examinations must be carried out at once.

(1) stool examination. The fecal occult blood test is not specific for the diagnosis of this disease, but the method is simple and easy, which can be used as a screening method or provide clues for early diagnosis.

(2) digital rectal examination. Low rectal cancer is far more common in China than abroad, accounting for 77.5% of rectal cancer, so most rectal cancer can be felt by rectal digital examination.

(3) sigmoidoscopy. 77.7% of colorectal cancer in China occurs in rectum and sigmoid colon. The commonly used sigmoid colonoscopy tube is 30cm long, which can directly find tumors below anal canal, rectum and sigmoid colon.

(4) X-ray barium enema examination. If the lesion is in the upper sigmoid colon or higher, X-ray barium enema should be performed. Ordinary barium enema X-ray examination is easy to miss the diagnosis of small intestinal cancer. It is best to use double contrast examination of gas and barium, which can improve the correct rate of radiological diagnosis and show the location and scope of the tumor.

(5) Fiberoptic colonoscopy. All the colon can be clearly observed, and suspicious lesions can be taken for pathological examination under direct vision, which is conducive to the early discovery of micro colon cancer and the diagnosis of cancer, and further improve the diagnostic accuracy of this disease. It is the most important examination method for colorectal cancer.

(6) Determination of serum carcinoembryonic antigen. Carcinoembryonic antigen (CEA) can be detected in the serum of patients with colorectal cancer. CEA is a glycoprotein that often appears in the serum of patients with malignant tumors, and is not a specific antigen related to colorectal cancer. Therefore, the determination of serum CEA is not specific for the diagnosis of this disease. The detection of CEA by radioimmunoassay and quantitative dynamic observation are of certain significance for judging the surgical effect of colorectal cancer and monitoring postoperative recurrence. For example, after the tumor is completely removed by surgery, the serum CEA gradually decreases; If it recurs, it can rise again.

(7) Other inspections. Intrarectal ultrasound scanning can clearly show the range, size, depth and surrounding tissues of rectal mass, and can distinguish the fine structure of each layer of rectal wall. The examination method is simple and can provide images quickly, which is helpful for the choice of surgical methods and postoperative follow-up.

CT examination is of great significance to understand the degree of extraintestinal invasion of tumor and whether there is lymph node or liver metastasis, and it is more accurate to diagnose the recurrence of rectal cancer.