Health Tips and Tricks

Occult gastrointestinal (GI) bleeding is by definition bleeding not apparent at inspection of the stools. As with overt GI bleeding, occult bleeding may be acute or chronic, intermittent, or continuous. There are many causes of occult bleeding. The site of bleeding may be at any anatomic level between the oropharynx and the anus. Occult bleeding often results from trivial pathologic conditions, but it can be a vital pointer to the presence of a health-threatening lesion. In practice then, the cause should be actively sought. A conservative, expectant approach is justified only when a serious pathologic condition has been excluded.
Iron deficiency is the most common cause of anemia worldwide. It often results from chronic GI blood loss,
especially among men and postmenopausal women in western-style societies and those with parasitic infections in less westernized countries. In the United States alone, 20 million persons have been estimated to have iron deficiency. The global prevalence of iron deficiency is estimated at 15%.
The clinician’s judgment is challenged in the face of the possibility or finding of occult GI bleeding. There are various reasons for this. There is a low level of endogenous physiologic blood loss into the GI tract of up to 1.5 mL per day; there are many possible sources of pathologic bleeding at many different possible sites; and the cause is not obvious. Confirmation of occult GI bleeding can be difficult at times, because some tests for occult bleeding lack ideal precision and accuracy. Abnormal results with qualitative tests are not always associated with pathologic changes, and negative results do not conclusively exclude low amounts of clinically significant bleeding. Furthermore, the biochemical characteristics of modification and degradation of hemoglobin and heme in the GI tract have only recently been elucidated in a way that is relevant to the correct use of fecal occult blood tests.
Many factors influence whether blood is visible. For instance, a drop of blood may be seen when bleeding is rectal in origin. Yet gastric bleeding might not be obvious to the patient unless it exceeds 50 mL and sometimes even 150 mL per day. The factors that influence this phenomenon include the amount and rate of bleeding, the lesion site, transit time, intralumenal degradative factors, the degree of attention patients pay to their stools. Patients are at risk for clinically significant iron deficiency when blood loss reaches 5 mL per day, although iron intake influences this amount.
Occult GI bleeding involves a defect in the continuity of the epithelium and thus may be due to inflammatory, neoplastic, infectious, vascular, externally induced, or traumatic mechanisms. As a group, acid peptic disorders are the most common cause of occult bleeding and anemia in western-style countries. Malignant tumors of the GI tract represent another frequent cause; colorectal cancer is the single most common lesion. On a global scale, however, hookworm infestation accounts for the largest number of persons with anemia from occult GI bleeding. Medications, especially aspirin and related nonsteroidal antiinflammatory drugs, commonly induce occult bleeding. Less common causes of occult bleeding include the heterogenous array of acquired and inherited vascular malformations, inflammatory bowel disease, and endurance sports, especially long-distance running.
The diagnosis of occult bleeding may be suggested by the finding of microcytic anemia with low iron stores or may be made directly by means of testing of feces for the derivatives of blood that remain as a result of the lumenal factors that cause degradation or modification of hemoglobin. Because clinically significant lesions do not always bleed and not all occult bleeding results in iron deficiency, hematologic and fecal blood assessment are complementary diagnostic tests and can be interpreted only in the context of all clinical information about the patient.
Several types of tests for blood in feces are available. Each has advantages and disadvantages that vary according to the clinical setting. These types are guaiac tests for heme, immunochemical tests for hemoglobin, heme-porphyrin assays for heme and heme-derived porphyrins, and radiochromium GI blood loss studies for blood volume loss. At present, the simple guaiac tests are the most widely used, but they are steadily being replaced by immunochemical tests when the clinical setting is appropriate. Whichever test is used, it must be carefully chosen to suite the clinical setting. Combining tests may be appropriate, and different tests may be used at different stages of the clinical evaluation.