Five guaiac-based tests for occult blood in faeces compared in vitro and in vivo

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Abstract
Five guaiac-based fecal occult blood tests (Fecatest, Fecatwin Sensitive, Fecatwin, Hemoccult, Hemafecia) were compared in vitro and in vivo and the effect of time between sample application and development of the color reaction was studied. In both types of experiments the sensitivity of Fecatest, Fecatwin Sensitive and Fecatwin was higher when the color reaction was developed at 24-72 h than at 2 h after application of the sample but for Hemoccult and Hemafecia the sensitivity in in vivo experiments was constant or tended to decrease with time. In upper gastrointestinal bleeding, false negative test results were obtained for Fecatest, Fecatwin Sensitive, Fecatwin, Hemoccult and Hemafecia in 21, 23, 38, 43 and 43%, respectively. In colorectal bleeding the corresponding percentages were 10, 10, 35, 35 and 35. Using the 51Cr-erythrocyte method, quantitative estimation of intestinal bleeding was performed in 20 patients with verified colorectal cancer and in 11 control patients. When the patient was bleeding from the left hemicolon, 29% of the Fecatwin, Hemoccult and Hemafecia test results were negative, 10% were negative for Fecatest and 14% for Fecatwin Sensitive. In patients with tumors in the right hemicolon, Fecatest and Fecatwin Sensitive were positive in all samples, whereas the other tests were negative in 10%. The proportion of false positives due to dietary factors correlates with the sensitivity of the tests.

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