Validity of immunological faecal occult blood screening for colorectal cancer: a follow up study

Immunological faecal occult blood testing has been recognised as a useful method for wide scale screening of colorectal cancer in Japan during the past few years. This study was carried out to evaluate the validity of an immunological faecal occult blood test for colorectal cancer screening.

A screening programme for colorectal cancer using an immunological faecal occult blood test was conducted on 3365 residents of regions within Nagano prefecture in 1991, and all the subjects were followed up for three years by verification from cancer registration. Based on the incidence of false negative cases among those who had been evaluated as normal by this screening, but were diagnosed as having colorectal cancer, the sensitivity and the specificity of this test were estimated.

Four false negative cases were found during the subsequent three year follow up period after screening. Among these four cases, one case was within the first follow up year, one case within the second year, and two cases within the third year. Accordingly, the sensitivity of this test was calculated as 90.9% within one year, 83.3% within two years, and 71.4% within three years, while the specificity was found to be 95.6%, indicating a validity higher than that achieved by a chemical occult blood test.

These findings suggest that the immunological faecal occult blood test has a high diagnostic accuracy and is a useful strategy for colorectal cancer screening.