Screening for Colorectal Neoplasias with Fecal Occult Blood Tests: False-positive Impact of Non-Dietary Restriction

Objective: Screening for colorectal cancer using guaiac-based fecal occult blood tests (gFOBT) is wellestablished in Western populations, but is hampered by poor patient compliance due to the imposed dietaryrestrictions. Fecal immunochemical tests (FIT) do not require dietary restriction, but are more expensive thangFOBT and therefore restrict its use in developing countries in Asia. However, Asian diets being low in meatcontent may not require diet restriction for gFOBT to achieve equivalent results. The objective of this study wasto evaluate and compare the validity and suitability of gFOBT and FIT or a combination of the two in screeningfor colorectal neoplasias without prior dietary restriction in an Asian population.
Methods: Patients referred tothe Endoscopic Unit for colonoscopy were recruited for the study. Stool samples were collected prior to bowelpreparation, and tested for occult blood with both gFOBT and FIT. Dietary restriction was not imposed. Toassess the validity of either tests or in combination to detect a neoplasm or cancer in the colon, their false positiverates, their sensitivity (true positive rate) and the specificity (true negative rate) were analyzed and compared.
Results: One hundred and three patients were analysed. The sensitivity for picking up any neoplasia was 53%for FIT, 40% for gFOBT and 23.3% for the combination. The sensitivities for picking up only carcinoma were77.8% , 66.7% and 55.5%, respectively. The specificity for excluding any neoplasia was 91.7% for FIT, 74% forgFOBT and 94.5% for a combination, whereas for excluding only carcinomas they were 84%, 73.4% and 93.6%.Of the 69 with normal colonoscopic findings, FOBT was positive in 4.3%, 23.2 %and 2.9% for FIT, gFOBT, orcombination of tests respectively.
Conclusion: FIT is the recommended method if we are to dispense with dietaryrestriction in our patients because of its relatively low-false positivity and better sensitivity and specificity rates.