Fecal Occult Blood Testing
The answer is that it depends. It depends on both the anatomic source and rate of bleeding. Large amounts of blood can be lost from upper GI sites and remain occult. Based on a number of observational studies with quantitative fecal blood tests, it takes more than 200mL/day for gastric bleeding to be uniformly overt, 150 mL/day from the cecum, 5-30 from the rectosigmoid, and just trace amounts from the anal canal (such as can commonly occur with hemorrhoids). So, bleeding rates can far exceed that required to produce iron deficiency and yet remain occult.
Quantity of GI Bleeding Required to "See" Blood
Jump to section:
- Occult Gastrointestinal (GI) Bleeding: Definition
- Quantity of GI Bleeding Required to "See" Blood in Stool
- Fecal Occult Blood Tests
- Why Detect Occult GI Bleeding?
- Causes of Fe Deficiency in Industrialized Countries (Average %)
- Causes of Occult GI Bleeding
- Fecal Detection of Ingested Blood
- Iron Deficiency or Anemia: Which Test?
- CRC Screening: Target Lesions
- Occult Bleeding From Colorectal Cancer
- Fecal Blood Testing for Colorectal Cancer (CRC)
- FOBT Screening
- Stool Test Detection of CRN in Screen Setting
- Laboratory Testing vs Office Digital Rectal Exam (DRE)
- Evaluation of Fecal Immunochemical Testing (FIT) Assays
- FIT Specificity
- CRC Screening by FOBTs
- CRC Screening Guidelines*
- CRC Screening: Which Fecal Blood Test?
- Soft Indications for FOBT Use?
- Fecal Occult Blood Tests Summary
- Mayo Medical Laboratories Tests