Immunological detection of faecal occult blood in colorectal cancer

A new two-phase test kit for faecal occult blood combining a sensitive guaiac test (Fecatwin (S)ensitive) with an immunological test for human haemoglobin (FECA-EIA) was compared with three current guaiac tests (Fecatest, Fecatwin, Haemoccult) in 19 colorectal cancer patients and 11 controls on a restricted diet. A total of 43 48 h faecal samples (30 from cancer patients and 13 from controls) were collected for quantitative determination of faecal blood loss with the 51Cr method. Qualitative testing revealed that FECA-EIA was the most sensitive test, giving one (3%) false negative test result in the 30 tests on colorectal cancer patients and no false positives in the control subjects. It was also the only test that detected low-degree tumour bleeding. Fecatest and Fecatwin S were the most sensitive guaiac tests, giving 7 and 10% false negative test results, respectively, in the 30 colorectal cancer samples, whereas Haemoccult and Fecatwin gave 23% false negative test results. For screening purposes and in order to reduce costs it is suggested that only the positive test results of the very sensitive guaiac test (Fecatwin S) should be tested with the FECA-EIA test to eliminate false positive results. With this approach the diagnostic accuracy of the new two-phase test will be about twice as good as for the Haemoccult test.