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PURPOSE: This study was conducted to clarify the diagnostic value of an immunochemical fecal occult blood test for hemorrhoids. PATIENTS AND METHODS: In a case-control study, an immunochemical fecal occult blood test with a 2-day method was carried out on 82 subjects with hemorrhoids, on 82 subjects with colorectal cancer, and on 82 healthy subjects. In a population-based cross-sectional study, 29,714 subjects who received an immunochemical occult blood screening with a 2-day method were divided into two groups, according to the results of a questionnaire on hemorrhoids, and the positivity rate of an immunochemical test as well as the predictive value for colorectal cancer were compared in the two groups. Moreover, both an immunochemical occult blood test with a 2-day method and colonoscopy were conducted at the same time on asymptomatic subject during a medical checkup. RESULTS: In the case-control study, the test was positive in 13.4% subjects with hemorrhoids, in 84.1% subjects with colorectal cancer, and in 4.9% healthy subjects, respectively, showing a significant difference in the detection rate between the two diseases (P [is less than] 0.001). In the population screening program, the test was positive in 6.9% subjects with hemorrhoids and in 6.5% subjects without hemorrhoids, and the predictive value was 3.2% in subjects with and without hemorrhoids, respectively, indicating no significant difference in the positivity rate as well as the predictive value between the two groups. Among 232 subjects in a medical checkup, 28 patients with hemorrhoids and 21 patients with colorectal polyp 1 cm or larger were diagnosed by colonoscopy, and the occult blood test was positive in 16.7% patients with hemorrhoids and in 52.4% patients with colorectal polyp, respectively. There was a significant difference in the sensitivity between the two disease groups (P [is less than]0.05). CONCLUSIONS: These findings indicate that the immunochemical fecal occult blood is unsuitable for the diagnosis of the patients with hemorrhoids and an examinition of the colorectum is necessary in cases where the occult blood test is positive but there is a sign of hemorrhoids. Am J Med. 1997;102: 551-554.[C] 1997 by Excerpta Medica, Inc.