Chronic lower gastrointestinal (GI) symptoms, including lower abdominal pain, bowel habit change, bleeding per rectum, and abdominal bloating, are caused by functional gastrointestinal disorders (FGID) and organic intestinal disorders, including colorectal cancer and chronic colitis. The presence of alarming features, such as the age of onset older than 50 years, rectal bleeding, anemia, significant weight loss, and family history of colorectal cancer, indicates organic diseases, and colonoscopy should be required. However, using only alarming features may not be sufficiently accurate. For example, anemia or significant weight loss, which are highly specific for organic disorders, usually occur in late-stage diseases. Conversely, the parameters with high sensitivity, such as the age of onset after 50 years, have a low specificity; colonoscopy in these patients may not be urgent. Therefore, tests that can help discriminate organic from functional diseases are warranted. Immunochemical fecal occult blood tests (iFOBT) and fecal calprotectin (FC) are biomarkers that indicate organic lesions in the gastrointestinal tract and could help diagnose patients with lower GI symptoms more accurately.

This study was a single-center, prospective cohort study undertaken at Siriraj hospital between March 2020 to November 2022. Eligible participants were required to collect their stool samples one to two days before the bowel preparation. The stool was sent for fresh smear examination, quantitative FIT (OC-SENSOR, EIKEN CHEMICAL, Japan), and quantitative fecal calprotectin (EliA Calprotectin 2, Phadia, Sweden). Blood samples were obtained on the day of the colonoscopy and were tested for complete blood count, albumin, and C-reactive protein (CRP) levels. In addition, clinical information was obtained, including alarm features such as the age of onset older than 50 years, rectal bleeding, anemia, significant weight loss, and family history of colorectal cancer. Colonoscopic findings and histopathological findings were used as the reference standard for diagnosis. We analyzed the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for diagnosing significant ileocolonic lesions, including colorectal cancer, advanced adenoma, and colitis, of each diagnostic modality comparing to the reference standard.

Inclusion criteria

• age of at least 18 years
• patients with at least one month of any lower gastrointestinal symptoms are as followings; lower abdominal pain, constipation, diarrhea, rectal bleeding, change in stool caliber, abdominal bloating,
• patients who are scheduled for a colonoscopy

Exclusion criteria

• incomplete colonoscopy
• incomplete stool collection

We enrolled adults older than 18 years with chronic lower GI symptoms for more than 1 month and were scheduled for a colonoscopy. The lower GI symptoms consisted of any of the followings; lower abdominal pain, constipation, diarrhea, rectal bleeding, change in stool caliber, and abdominal bloating. The stool samples were collected one to two days before the bowel preparation. All patients provided written informed consent. Patients who did not return their stool samples and whose complete colonoscopy was not achieved were excluded.