Comparative analysis of results of guaiac and immunochemical tests for faecal occult blood in colorectal cancer screening in two oncological institutions

The performances of three faecal occult blood tests, rehydrated Hemoccult (HOR), Hemoccult sensa (HOS) and Hemeselect (HSEL) on 3 days were compared in 1,725 subjects consecutively recruited in two oncological institutions in Milan and Florence. Significant differences between the results were evident as far as HOR positivity rates (7.5% vs 4.0%, respectively) and specificity (94.3% vs 97.5%, respectively) are concerned. Overall positivity rates of HOR, HOS and HSEL were 5.9%, 5.4% and 12%, respectively; significant differences were evident between HSEL and each of the two guaiac tests. Cancer was detected in eight subjects, adenoma's in 47. Specificity estimates were 95.8%, 90.2% and 90.5% for HOR, HOS and HSEL, respectively; significant differences were evident between HSEL and the other two tests. No significant difference between tests was evident for sensitivity or positive predictive values for cancer or adenomas. In the CSPO (Florence) population (1,223 subjects; five with cancer, 16 with adenoma's) the performances of 1-day HSEL testing were determined on the basis of the first faecal sample only and compared with 3-day HOR, HOS and HSEL testing. The positivity rates of 1-day HSEL, 3-day HOR, HOS and HSEL testing were 7.0%, 5.0%, 5.5% and 12.9%, respectively. Only 3-day HSEL positivity rate was significantly higher than 1-day HSEL. One-day HSEL specificity (94.9%) was significantly higher than 3-day HSEL (90.0%), whereas no significant difference was seen between 1-day HSEL, HOR (96.5%), and HOS (96.1%) specificity. No significant difference between tests is evident in the CSPO population as far as positive predictive values and sensitivity for cancer and adenomas are concerned. Our study suggests that 3-day HSEL is more sensitive than guaiac tests; however, due to its low specificity, the use of this test in a population-based screening programme may be criticised. In contrast, our preliminary evaluation suggests that 1-day HSEL is almost as specific as guaiac tests and almost as sensitive as 3-day HSEL. These results need to be confirmed in a population-based screening programme.