Sensitivity of immunochemical fecal occult blood test for colorectal flat adenomas

To assess the sensitivity of an immunochemical fecal occult blood test for colorectal flat adenomas, and to determine the relation between the size of flat adenomas and the results of this test.

Eleven colorectal flat adenomas under 1cm, 18 flat adenomas 1cm or larger, 187 polypoid adenomas under 1cm, 42 polypoid adenomas 1cm or larger and 144 healthy controls were investigated. Each subject was tested with an immunochemical occult blood test on two consecutive days, and the accuracy of this test was evaluated.

The sensitivity of this test was 18% for flat adenomas under 1cm, 67% for flat adenomas 1cm or more, 19% for polypoid adenomas under 1cm and 60% for polypoid adenomas 1cm or more. Specificity was 95%, showing a significant difference in the sensitivity between flat adenomas 1cm or more and those under 1cm (p<0.05) as well as a significant difference between flat adenomas 1cm or more and polypoid adenomas under 1cm (p<0.001), whereas no significant difference was seen in the sensitivity between flat adenomas 1cm or more and polypoid adenomas 1cm or more.

These results indicate that the sensitivity of immunochemical occult test for flat adenomas was similar to the sensitivity for common polypoid adenomas. The size of adenomas is a more important morphological factor for determining the sensitivity of this fecal occult blood test.