Immunological fecal occult blood test vs. serum ferritin for detection of colorectal neoplasia in high risk asymptomatic population.

INTRODUCTION: Fecal occult blood tests (FOBT) (biochemical or immunological) are based on the fact that most of the polyps or cancers bleed. Anemia due to iron deficiency is a wellknown sign for colorectal cancer (CRC). Ferritin is frequently used to select candidates for colonoscopy.
OBJECTIVE: To determine and compare the diagnostic value of immunological fecal occult blood test vs. ferritin for the detection of colorectal neoplasia (cancer or polyps) in high-risk patients.
METHODS: A transversal prospective study at National Cancer Institute, Mexico City, in consecutive asymptomatic subjects at high risk for CRC was performed, comparing two tests (immunological against serum ferritin) with colonoscopy plus histopathology. Both tests were performed in a blindly fashion previous to colonoscopy.
RESULTS: Fifty patients were included in the study; twenty-eight patients had colorectal neoplasia (21 CRC, 7 adenomas). All immunologic tests for fecaloccult blood were positive in patients with colorectal lesions (sensitivity, 98%). There was no difference between the mean ferritin levels in patients with CRC or adenomas vs. those with negative colonoscopy (p = 0.58). The cutoff point where significant relationship between serum ferritin levels and colon lesions was established was ?46 ng/mL. In anemic patients with serum ferritin levels <46 ng/mL, the test had a sensitivity 53%, specificity 86%, positive predictive value 83%, and negative predictive value of 59% (p = 0.003).
CONCLUSIONS: The immunological FOBT is a better diagnostic tool than serum ferritin for screening of colonic neoplasms.