Fecal occult blood tests in occult gastrointestinal bleeding.

Occult gastrointestinal bleeding is diagnosed by using one of the commercially available fecal occult blood tests (FOBTs). Guaiac-based slide tests are most frequently used, although the more specific immunochemical methods are promising. The guaiac tests are inexpensive, nonspecific, qualitative measures of stool blood, and their use requires dietary and drug restrictions. Clinicians need to be aware of the causes of false-positive and false-negative test results. Although specific for the presence of human blood, immunochemical tests are more expensive and tend to react also to physiological quantities of blood in fecal specimens. Whichever test is chosen, it must be processed and read correctly. Annual FOBT screening for colorectal cancer, combined with periodic flexible sigmoidoscopy, is a cost-effective method of detecting early, curable colorectal cancer.