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

Five guaiac-based faecal occult blood tests (Fecatest, Fecatwin Sensitive, Fecatwin, Haemoccult, Hemafecia) were compared in vitro and in vivo and the effect of time between sample application and development of the colour reaction was studied. In both type of experiments the sensitivity of Fecatest, Fecatwin Sensitive and Fecatwin was higher when the colour reaction was developed at 24-72 h than at 2 h after application of the sample but for Haemoccult 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, Haemoccult 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 left hemicolon 29% of the Fecatwin, Haemoccult and Hemafecia test results were negative, 10% were negative for Fecatest and 14% for Fecatwin Sensitive. In patients with tumours in right hemicolon Fecatest and Fecatwin Sensitive were positive in all samples, whereas the other tests were negative in 10%. Experiments revealed that the proportion of false positives due to dietary factors correlated with the sensitivity of the tests.