Fecal Occult Blood Testing
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The following questions were submitted by viewers and answered by the presenters, David A. Ahlquist, MD, Professor of Medicine and Consultant in Gastroenterology, and Amy K. Saenger, PhD, Assistant Professor of Laboratory Medicine and Pathology and Director of Cardiovascular Laboratory Medicine in the Department of Laboratory Medicine and Pathology, both at Mayo Clinic in Rochester, Minnesota. Questions are presented as submitted (unedited).
How do you discourage the practice of digital rectal exam (DRE) in the ED and throughout the hospital?
Based on the best data at hand, DRE cannot be recommended for either colorectal cancer screening or the workup of anemia. The most effective and durable strategy to translate evidence-based recommendations into practice is through rational policy change and education. As an institution with active continuous improvement efforts, Mayo Clinic supported the initiative to examine current fecal blood testing practices against the context of new clinical data. After review of the evidence, the Department of Laboratory Medicine and Pathology along with Clinical Practice Committees at multiple division and departmental levels recommended discontinuation of DRE in both outpatient and hospital settings. Acculturation of these changes will require time and continued educational efforts.
If the digital rectal exam (DRE) in the physician's office is of limited value, is there any value to performing this test in the emergency room (sample obtained by DRE) on a stat basis using the guaiac slides?
There are 2 dominant indications for fecal occult blood testing.... One is colorectal cancer screening and the other is the evaluation of anemia or iron deficiency. It could be argued that neither of these is ever an emergency. And, use of DRE for either is inappropriate because of poor quality control. There are no sound outcomes data to support off-label use of fecal occult blood tests for assessment of gross bleeding (hematochezia or melena) by guaiac testing of stool on DRE. In face of acute GI bleeding, the choice of an emergency intervention such as endoscopy or blood replacement is based on hemodynamic and hematologic data rather than on the presence of rectal blood. Off-label use of guaiac tests in the emergency room setting should be limited to algorithms endorsed by clinical leaders in that setting.
How compliant are the patients in collection of stool specimens for this procedure?
Patient compliance to fecal testing, if ordered and recommended by a healthcare provider, is very high. In an older Mayo Clinic study looking at compliance to HemoQuant testing ordered in the outpatient setting, specimen return rates were 97% (Ann Intern Med 1988;108:609-612).
Is fecal immunochemical testing (FIT) vs HemoQuant useful to discriminate between upper and lower source of bleeding in someone who initial screens fail to identify lesion?
It is a logical thought, as FIT is quite specific for lower GI bleeding and HemoQuant detects bleeding from throughout the GI tract equally well. A decision to use this approach in practice would be based on data, and I am not aware of any studies addressing this concept.
What are the other tests needed to finalize the colorectal cancer (CRC) diagnosis?
A positive fecal occult blood test used for the indication of CRC screening should be followed up with colonoscopy. In the future, there may be other noninvasive tools (such as molecular stool or plasma tests) as the initial screening tool, and these also would be followed up with colonoscopy if positive.