J Med Assoc Thai 2019; 102 (2):18

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The Prevention of Development of Colorectal Cancer by Colonoscopy after Positive Fecal Occult Blood Test
Rakchob T Mail, Supsamutchai C , Teerapradith J , Promboon T , Chiemsombat P , Choikrua P , Jirasiritham J

Background: Fecal occult blood tests (FOBTs) have been known as a colorectal cancer (CRC) screening tool for 30 years. Because of the reasonable price and simplicity, the test is used to the present. However, fecal occult blood tests have low specificity to the human blood and colonoscopy is superior in colorectal cancer screening. Now, the use of fecal occult blood tests as screening tool has been questioned.

Objective: To demonstrate that FOBTs have a role in improving diagnostic performance in colorectal cancer screening.

Materials and Methods: Retrospective chart review of patients who were screening for colorectal cancer by FOBT and colonoscopy was performed from January 2006 to December 2015 in Ramathibodi Hospital. Patients with a history of CRC, incomplete colonoscopy and inflammatory bowel disease were excluded. Result of FOBT and colonoscopy were collected including pathological finding, size and location of the lesion.

Results: 2,043 patients were included in this study. FOBT positive rate was 48.89% and cancer was found in this group 99 of 999
patients (9.9%). Positive predictive value (PPV), negative predictive value (NPV) and sensitivity of positive FOBTs for the cancer were 10 (8.2 to 12), 98.3 (97.3 to 99) and 84.6% (76.8 to 90.6), respectively. Positive predictive value (PPV), negative predictive
value (NPV) and sensitivity of positive FOBTs for advanced adenoma and cancer were 12.5 (10.5 to 14.7), 96.6 (95.4 to 97.7) and 78.1% (70.9 to 84.3), respectively. Sensitivity was increased with the larger size and number of polyps; moreover sensitivity was highest in the left side colon (53.6%).

Conclusion: In our study showed positive FOBTs has high sensitivity for colorectal cancer screening (84.6%) with acceptable PPV (10). With the advantage of the FOBTs, non-invasive, low cost and easy-to-used method, FOBTs should be considered for first step CRC screening. However, the high false positive rate of this test must be made aware.

Keywords: Colorectal cancer screening, Colorectal polyp, Fecal occult blood test

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