Evaluation of the optimum cut-off point in immunochemical occult blood testing in screening for colorectal cancer.

This study was carried out to assess, from the aspects of cost-effectiveness and diagnostic validity, the optimum cut-off point for immunochemical occult blood testing using a 2-day method as a means of screening for colorectal cancer. Four thousand, two hundred and sixty asymptomatic individuals were subjects of this study. They gave samples for an immunochemical fecal occult blood test, and colonoscopy was carried out during a medical check-up. For evaluation of the optimum cut-off point, three cut-off levels of fecal haemoglobin, 50, 150 and 300 ng/ml, were used. A total of 27 patients with colorectal cancer were diagnosed. The average costs to detect one patient with colorectal cancer and the sensitivity and specificity of these three cut-off points of fecal haemoglobin were evaluated. The average costs for the detection of one cancer case were calculated as $2870.45 for cut-off level of 50 ng/ml, $2492.98 for that of 150 ng/ml and $3329.09 for that of 300 ng/ml, respectively. The sensitivity and specificity were calculated as 89 and 94% for the 50 ng/ml cut-off level, 81% and 96% for the 150 ng/ml cut-off level and 56 and 97% for the 300 ng/ml cut-off level, respectively, indicating a significant difference in the sensitivity between the 50 and 300 ng/ml levels (P<0.05), as well as between the 150 and 300 ng/ml levels (P<0.05), and a significant difference in the specificity between the 50 and 300 ng/ml levels (P<0.05). However, no significant difference was observed in the specificity between the 50 and 150 ng/ml levels. The findings show that 150 ng/ml of fecal haemoglobin is the optimal cut-off point when carrying out the OC-Hemodia test as a means of screening for colorectal cancer.