A 10-year-old boy is brought to the office due to exertional fatigue and exercise intolerance lasting 2 months. The patient denies black and tarry stools, hematochezia, or abdominal pain. He has no chronic medical conditions and takes no medications or supplements. Temperature is 36.9 C (98.4 F), blood pressure is 110/78 mm Hg, and pulse is 86/min. Mucosal pallor is present. There is no lymphadenopathy. The abdomen is soft and nontender, without palpable masses. Stool is positive for occult blood. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 9.4 g/dL |
| Mean corpuscular volume | 74 µm3 |
| Platelets | 380,000/mm3 |
| Leukocytes | 7,500/mm3 |
Coagulation studies and erythrocyte sedimentation rate are within normal limits. Upper endoscopy and colonoscopy, including biopsies, are unremarkable. Which of the following studies is most likely to reveal this patient's diagnosis?
Show Explanatory Sources
This patient with findings of iron deficiency anemia (eg, fatigue, exercise intolerance, pallor, microcytosis) has a positive fecal occult blood test (FOBT), making occult gastrointestinal (GI) bleeding the most likely cause of his symptoms.
Patients with occult GI bleeding, defined as a positive FOBT and/or iron deficiency anemia without visible bleeding (eg, hematemesis, melena, hematochezia), should first be evaluated by upper endoscopy and colonoscopy to localize the source of blood loss. When colonoscopy and upper endoscopy are unremarkable, as in this patient, small bowel pathology should be considered.
In children, the most likely cause of small bowel bleeding is Meckel diverticulum, which results from failed closure of the vitelline duct during early embryogenesis. Although most commonly seen in children age <2, it can present at an older age, including in adolescence. Secretion of hydrochloric acid from ectopic gastric tissue within the diverticulum causes intestinal ulceration, which can lead to either occult bleeding or painless hematochezia. Because the diverticulum is in the small intestine, it may not be detected on upper endoscopy or colonoscopy.
Therefore, initial evaluation of occult, small bowel bleeding in a child is often done with a Meckel scan, which uses technetium 99m pertechnetate to detect gastric mucosa. Video capsule endoscopy may also be used to evaluate occult, small bowel bleeding and can help identify angiodysplasia or neoplasia.
(Choice A) Because it detects brisk GI bleeding, CT angiography usually misses slower occult bleeding and would therefore be less helpful for this patient. CT angiography could have been considered had this patient presented with brisk GI bleeding (eg, hematochezia, melena, and/or hematemesis in the setting of hemodynamic instability).
(Choice B) Fecal calprotectin, a protein found within neutrophils, is typically positive in patients with inflammatory bowel disease, but symptoms of hematochezia, abdominal pain, diarrhea, and/or weight loss would be expected. Colonoscopy findings of intestinal inflammation are also common.
(Choice C) Fecal DNA testing is used as a screening tool for colorectal cancer mainly in patients at average risk for colon cancer (eg, age >45). It is not typically used in children.
(Choice E) Tissue transglutaminase antibody titers are used to screen for celiac disease, which can cause microcytic anemia due to iron malabsorption. However, FOBT testing would be negative because celiac disease does not usually cause GI bleeding.
Educational objective:
Small bowel pathology should be considered when the initial evaluation of occult gastrointestinal bleeding by upper endoscopy and colonoscopy fails to identify the source of blood loss. Meckel diverticulum is the most likely cause of small bowel bleeding in a child and can be diagnosed by technetium 99m pertechnetate scan. Video capsule endoscopy can also be considered to assess for angiodysplasia and neoplasia.