What is the role of stool testing in the diagnosis of iron deficiency anemia?

Updated: Sep 07, 2019
  • Author: James L Harper, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Testing stool for the presence of hemoglobin is useful in establishing gastrointestinal (GI) bleeding as the etiology of iron deficiency anemia. Usually, chemical testing that detects more than 20 mL of blood loss daily from the upper GI tract is employed. More sensitive tests are available; however, they produce a high incidence of false-positive results in people who eat meat. Severe iron deficiency anemia can occur in patients with a persistent loss of less than 20 mL/d.

To detect blood loss, the patient can be placed on a strict vegetarian diet for 3-5 days and the stool can be tested for hemoglobin with a benzidine method, or red blood cells (RBCs) can be radiolabeled with radiochromium and retransfused. Stools are collected, and the radioactivity is quantified in a gamma-detector and compared to the radioactivity in a measured quantity of the patient’s blood. An immunologic method of detecting human species-specific hemoglobin in stool is under development and could increase specificity and sensitivity.

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