Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1088 page)

NONINVASIVE PRENATAL TESTING (NIPT)

See Prenatal Screening, Noninvasive.

OCCULT BLOOD, STOOL

   Definition

   Occult bleeding refers to the initial presentation of a positive fecal occult blood test (FOBT) result and/or iron deficiency anemia, when there is no evidence of visible blood loss to the patient or physician. The differential diagnosis for occult GI bleeding is broad. Some of the more common causes include colon cancer, esophagitis, peptic ulcers, gastritis, inflammatory bowel disease, vascular ectasias, portal hypertensive gastropathy, and gastric antral vascular ectasias. However, less common causes such as gastroesophageal cancers, hemosuccus pancreaticus, hemobilia, and infections also need to be considered. Non-GI sources of blood loss such as hemoptysis and epistaxis can also cause a positive FOBT. FOBT falls into two primary categories based on the detected analyte: guaiac based (gFOBT) and immunoassay based (FIT). gFOBT are the most common stool blood tests in use for colorectal cancer screening, and they detect blood in the stool through the pseudoperoxidase activity of heme or hemoglobin, whereas immunochemical-based tests react to human globin.

   
Normal range:
negative.

   Use

   Screens for carcinomas (particularly colon) and polyps of the GI tract

   Identifies GI bleeding related to upper GI bleeding (gastric ulcer)

   Screens for diverticulitis and colitis

   Interpretation

Increased In

   GI malignancies (colon)

   Diverticular disease

   GI polyps

   Ischemic bowel disease

   Inflammatory lesions (ulcerative colitis, Crohn disease, shigellosis, amebiasis)