Random comparison of guaiac and immunochemical fecal occult blood tests for colorectal cancer in a screening population

Gastroenterology. 2008 Jul;135(1):82-90. doi: 10.1053/j.gastro.2008.03.040. Epub 2008 Mar 25.


Background & aims: Despite poor performance, guaiac-based fecal occult blood tests (G-FOBT) are most frequently implemented for colorectal cancer screening. Immunochemical fecal occult blood tests (I-FOBT) are claimed to perform better, without randomized comparison in screening populations. Our aim was to randomly compare G-FOBT with I-FOBT in a screening population.

Methods: We conducted a population-based study on a random sample of 20,623 individuals 50-75 years of age, randomized to either G-FOBT (Hemoccult-II) or I-FOBT (OC-Sensor). Tests and invitations were sent together. For I-FOBT, the standard cutoff of 100 ng/ml was used. Positive FOBTs were verified with colonoscopy. Advanced adenomas were defined as >or=10 mm, high-grade dysplasia, or >or=20% villous component.

Results: There were 10,993 tests returned: 4836 (46.9%) G-FOBTs and 6157 (59.6%) I-FOBTs. The participation rate difference was 12.7% (P < .01). Of G-FOBTs, 117 (2.4%) were positive versus 339 (5.5%) of I-FOBTs. The positivity rate difference was 3.1% (P < .01). Cancer and advanced adenomas were found, respectively, in 11 and 48 of G-FOBTs and in 24 and 121 of I-FOBTs. Differences in positive predictive value for cancer and advanced adenomas and cancer were, respectively, 2.1% (P = .4) and -3.6% (P = .5). Differences in specificities favor G-FOBT and were, respectively, 2.3% (P < .01) and -1.3% (P < .01). Differences in intention-to-screen detection rates favor I-FOBT and were, respectively, 0.1% (P < .05) and 0.9% (P < .01).

Conclusions: The number-to-scope to find 1 cancer was comparable between the tests. However, participation and detection rates for advanced adenomas and cancer were significantly higher for I-FOBT. G-FOBT significantly underestimates the prevalence of advanced adenomas and cancer in the screening population compared with I-FOBT.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoma / diagnosis*
  • Adenoma / epidemiology
  • Aged
  • Colonic Polyps / diagnosis
  • Colonic Polyps / epidemiology
  • Colonoscopy
  • Colorectal Neoplasms / diagnosis*
  • Colorectal Neoplasms / epidemiology
  • Female
  • Guaiac*
  • Humans
  • Immunohistochemistry*
  • Indicators and Reagents
  • Male
  • Mass Screening / methods*
  • Middle Aged
  • Occult Blood*
  • Patient Selection
  • Predictive Value of Tests
  • Prevalence
  • Prospective Studies


  • Indicators and Reagents
  • Guaiac

Associated data

  • ISRCTN/ISRCTN57917442