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Am Fam Physician. 2004;69(5):1263

The use of fecal occult blood testing has been recommended as a screen for colorectal cancer in patients at average risk. This recommendation is based on the fact that screening with fecal occult blood testing has been shown to reduce mortality from colorectal cancer by 15 to 33 percent. The standard guaiac-based fecal occult blood tests have some shortcomings, including poor patient compliance, the need for dietary and medication restrictions, and poor sensitivity and specificity. The guaiac-based tests also have a low positive predictive value that results in a substantial number of normal follow-up examinations after a positive test result. Newer tests are based on immunochemical detection of human blood in the stool. They have better specificities and higher positive predictive values than the guaiac-based fecal occult blood tests. Although the immunochemical-based tests have better statistics, no studies have compared the guaiac-based tests with the immunochemical-based tests. Ko and associates compared the level of patient compliance and test characteristics of the guaiac-based fecal occult blood tests with the immunochemical-based fecal occult blood tests.

The study was performed in a general medicine clinic of a Veterans Affairs health system. Fecal occult blood tests were ordered if the patient had not had this test within the past year or had not had lower gastrointestinal endoscopy within the previous five years. The health system was divided into two groups with similar patient and physician characteristics. An automated system was used to remind the nurses to order colorectal screening. One group used immunochemical-based tests, while the other group used guaiac-based tests. Patients received instructions on how to perform the test and were sent home with the screening kits. Test cards were returned, and any positive results were referred automatically to each patient’s primary care physician. The outcomes measured included completion and positivity rates, time to test completion, completion of diagnostic follow-up, and positive predictive values.

Of the study population, 2,965 patients received immunochemical-based tests and 2,964 received guaiac-based tests. The groups had similar return rates; 48 percent of immunochemical-based cards and 47 percent of guaiac-based cards were returned. The positivity rate for both groups was 9 percent. In patients who had positive test results and further colon evaluation, the proportion of any type of polyps, adenomas, adenomas greater than 1 cm, and colorectal malignancies discovered were similar in both groups. A total of 21 carcinomas were discovered in the study groups.

The authors conclude that the immuno-chemical-based and guaiac-based tests for fecal occult blood had similar performances in detecting colorectal abnormalities. Even though the immunochemical-based test is simpler to perform, patient compliance was similar between the groups. Because these two tests had similar rates of patient compliance and positive predictive values, use of the more expensive immunochemical-based test may not be indicated in general practice.

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