Performance characteristics and comparison of two immunochemical and two guaiac fecal occult blood screening tests for colorectal neoplasia.

A new immunochemical test for stool Hb, FlexSure OBT, was compared with the immunochemical HemeSelect and guaiac Hemoccult II and Hemoccult SENSA tests. Blinded development of test cards smeared with stools having added human blood showed better analytical sensitivity of FlexSure OBT (0.2 ml blood/100 g feces), than Hemoccult SENSA (> or =0.5 ml) or Hemoccult II (> or =1.0 ml). All four stool tests were prepared by 403 subjects having endoscopic examinations. The guaiac tests and FlexSure OBT were easy to prepare and develop. The positivity rate of Hemoccult SENSA was 8.7%, Hemoccult II 6%, FlexSure OBT 4.2%, and HemeSelect 3.4%. In this mainly asymptomatic (97%) population, 98% were free of clinically significant neoplasia (five had cancers, three had adenomas > or =1.0 cm). Sensitivity for cancers or adenomas > or =1.0 cm was similar for all tests (62.5-86%, NS) and Hemoccult SENSA had the lowest specificity (92% vs 95-98%, P < 0.05); but both Hemoccult II and Hemoccult SENSA had significantly lower predictive positive values (21% and 14%) than either FlexSure OBT (29%) or HemeSelect (50%) (P < 0.05). If both Hemoccult SENSA and FlexSure OBT were positive in the same subjects (1.7%), sensitivity for cancer or adenomas > or =1.0 cm (50%) was not significantly better than guaiac tests, but specificity (99.2%) and predictive positive (57%) values were improved (P < 0.05). In this population, guaiac tests were as sensitive as immunochemical tests for clinically significant colorectal neoplasia, but with significantly lower predictive positive values. A combination of a sensitive guaiac test (Hemoccult SENSA) and a specific confirmatory test for human Hb (FlexSure OBT) provided high specificity, comparable to HemeSelect.