A comparative study of fecal occult blood tests for early detection of gastrointestinal pathology

Article Abstract:

Testing the feces for hidden (occult) blood is one of the methods by which a physician may hope to identify abnormal conditions in the gastrointestinal tract before other more serious symptoms appear. However, the best way to test for fecal occult blood is a hotly debated subject, and little effort has been given to making direct comparisons of different testing methods. To compare different fecal blood testing methods, 120 patients were screened using five slide tests: Monohaem, Fecatwin S/Feca, Coloscreen III, Coloscreen III/VPI, and an enzyme-linked immunosorbent assay (ELISA). The patients were also evaluated by independent methods, such as colonoscopy and air contrast barium enema, for conditions which would likely result in bleeding. Such conditions were identified in a total of 73 patients; esophagitis, gastritis, and/or duodenitis were the most common conditions. The Monohaem test had no false positive and nine false negative results; the other tests had both false positive and false negative results. To simplify the presentation of the data, the values for false negatives were mathematically combined into a single number called the test efficiency. The Monohaem test had the highest score with an efficiency of 87 percent; other scores included Coloscreen III with 79 percent, Coloscreen II/VPI with 82 percent, Fecatwin S with 68 percent, and the ELISA having an efficiency of 77 percent. Different tests could be used together to achieve higher efficiencies. Considered together, Coloscreen III, Fecatwin, and Monohaem had an efficiency of 93 percent. The results indicate that the immunological tests, such as Monohaem and ELISA, had excellent predictive values; positive test results were highly indicative of a bleeding gastrointestinal lesion. However, none of the tests had satisfactorily low levels of false negatives, indicating that any screening program based only upon fecal occult blood testing will be certain to miss patients with bleeding lesions. (Consumer Summary produced by Reliance Medical Information, Inc.)

Medical examination, Feces, Blood, Blood tests

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Colorectal cancer detection in the practice setting: impact of fecal blood testing

Article Abstract:

Colorectal cancer is a major cause of cancer deaths in the developed countries. Unfortunately, rapid, inexpensive, and reliable procedures do not exist to detect colorectal cancer as they do for other cancers, such as cancer of the cervix. The National Cancer Institute and the American Cancer Society recommend that patients over 50 receive a yearly test for the presence of occult blood in their feces, which may indicate colorectal cancer or other gastrointestinal lesions. However, other groups, such as the United States Preventive Services Task Force indicate that these recommendations are based on opinion rather than on established evidence. In a retrospective examination of the records of 160 cases of colorectal cancer with a preceding stool test, the effectiveness of testing for occult blood as a diagnostic screening test was evaluated. In 71 percent of the cases, there was clear evidence of colorectal problems at initial examination; in many of these cases, the test for fetal occult blood was normal. Overall, 40 percent of the patients had normal results using the HemoQuant test for occult blood. In only 16 percent of the patients was a positive test for occult blood the only initial sign of colorectal cancer. However, these patients tended to have disease in earlier stages, and were thus better prospects for treatment. The results show that for some patients, the fecal occult blood test may be very important. However, most colorectal cancer patients are diagnosed without the results of a fecal blood test. In addition, considering the high percentage of cancers which are not detected by the test, this test cannot be considered to be an effective screening device. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Limitations of fecal occult blood testing

Article Abstract:

There are numerous studies on the testing of feces for traces of hidden (occult) blood. In the May 1990 issue of the Archives of Internal Medicine, two more studies are added to this list. Unfortunately, these studies highlight not only problems with the test, but also the difficulty in properly designing and reporting research on fecal occult blood testing. In the article by Ahlquist et al., 41 percent of patients with symptomatic colorectal cancer tested negative with HemoQuant, a sensitive test for gastrointestinal bleeding. The article by Stelling and colleagues ambitiously tried to examine the role of fecal blood testing in virtually all gastrointestinal pathology, but the study suffered from ambiguities in patient selection and treatment, which make full interpretation difficult. It is clear that the early detection of gastrointestinal disease is important, but it is equally clear that, although fecal occult blood testing is a valuable tool, such testing is insufficient as a stand-alone screening test. Inclusion of other tests, such as sigmoidoscopic examination, are necessary if a screening program is to have significant impact upon mortality due to colorectal cancer. (Consumer Summary produced by Reliance Medical Information, Inc.)

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