Characteristics of colorectal cancer: MATERIALS AND METHODS
Subjects for the cross-sectional study were selected from participants in an annual employee medical checkup from April 1, 1990 to March 31, 1999. The two hospitals for the medical checkups were located in central Nagano Prefecture. Physicians from the department of endoscopy of each hospital carried out both colonoscopy and immunochemical fecal occult blood testing using two separate stool samples on all participants, without dietary or medicinal restriction. Participants who had a history of recent rectal bleeding or any symptoms of colorectal diseases before the examination were excluded from the study. Fecal occult blood testing was performed on stool specimens obtained during the digital rectal examination. If the rectal ampulla of the participants was empty, mucus obtained by digital rectal examination was used for the occult blood test. All patients with colorectal cancer diagnosed by colonoscopy were divided into two groups, according to the results of the fecal occult blood test; intergroup comparisons were made in terms of individual factors, such as site, size, Dukes classification and histological type of the cancer lesions. The final diagnosis of colorectal cancer was made after surgical or endoscopic removal of tumours.
The immunochemical fecal occult blood test was performed by a trained technician at the hospital laboratory. The principles and procedures of the immunochemical slide Imdia-HemSp (FujiRebio, Japan) (a reversed passive hemagglutination test), which was used in the present investigation, are outlined as follows. The test subjects were first instructed to make a thin fecal smear on the test filter paper. Disks of the specimens from the feces-smeared slides were placed in round wells in a microtitre plate. A diluent was added to extract the specimens from the disks. A portion of the extract was removed and diluted serially in the next three wells of the plate. Erythrocytes coated with antihuman hemoglobin antibody were added to the last wells, and the mixture was incubated at room temperature for 30 min. Samples showing agglutination at a dilution of 1:8 were interpreted as a positive result. The absence of agglutination was interpreted as a negative result. The procedures of this test are uncomplicated, and the cost per slide for each test is approximately US$4.00 (¥440; average exchange rate was US$1=¥110 during the period of the investigation).
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Statistical analysis was performed by %2 test, and a twotailed P value of less than 0.05 was defined as statistically significant.