Overview of Gastrointestinal Bleeding
Bleeding
is a common symptom of both benign and malignant disorders of the digestive
system. Bleeding, even in the absence of other digestive tract symptoms such as
pain, obstruction, or signs of perforation, always warrants a definitive
evaluation because it may lead to a life-threatening loss of blood and is often
associated with significant and/or potentially lethal disorders. The more
evidence there is of bleeding (anemia, iron deficiency, or overt bleeding) the
greater the likelihood that a serious disorder is present. Advanced malignancies
are common causes of bleeding, but most causes are benign and treatable with
medication and/or endoscopic techniques.
Evaluation of the cause of bleeding includes consideration
of the location of gastrointestinal bleeding; one must also assess the severity
and rapidity of blood loss. Blood loss from the digestive tract is described as
overt when there is obvious bleeding and occult when bleeding can only be
detected by stool testing, a drop in hemoglobin, or iron deficiency.
Overt bleeding from the upper digestive system presenting
as the vomiting of bright-red blood is hematemesis. Partially digested
blood that has turned black appears in vomitus as black strands of mucoid
material or small specks of black described as coffee ground emesis. Bright-red
blood expelled from the rectum is hematochezia. Passage of black stool
from overt bleeding is melena, which has a distinctive odor well known
to gastroenterologists and emergency physicians as an urgent call for prompt
intervention. Hematochezia may be seen as droplets or staining of the toilet
paper when it originates from rectal cancer or hemorrhoids, or it may fill the
toilet bowel. In either situation, endoscopic diagnosis of the cause is
necessary.
Bleeding is often not recognized until a patient is found
to be anemic by physical examination or laboratory tests. Iron deficiency in
males of any age and all non menstruating females is commonly due to bleeding.
Although iron deficiency in premenopausal women is more commonly due to
menstruation, gastrointestinal bleeding should always be considered.
Malabsorption is also a common cause of iron deficiency. This is particularly
common in patients with celiac disease and chronic gastric hypochlorhydria
whether due to severe atrophic gastritis or to chronic use of high-dose proton
pump inhibitors. Differentiating occult bleeding from malabsorption is
facilitated by point-of-service stool testing for blood with paper tests that
react to the presence of any oxidating substance (stool guaiac test) or
immune reactions (fecal immune test for hemoglobin); the latter test is
much more specific but less sensitive for upper gastrointestinal sources and
more expensive. When blood is found, a diagnosis should always be sought.
Distinguishing between occult bleeding and malabsorption is difficult because
bleeding from most lesions is intermittent. For example, in patients with known
colon cancer extensive enough to require surgical resection, only one in four
stool tests for occult blood will be positive. The limited sensitivity of these
tests necessitates repeating stool examinations in four to six specimens 2 or 3
days before one can be confident there is no active bleeding. Repeat testing of
stools, hemoglobin levels, and iron levels; keen judgment; and close follow-up
are necessary when evaluating patients with suspected occult bleeding.
The most challenging patients are those who have
documented bleeding but for whom a definitive cause is elusive. The term occult
gastrointestinal bleeding is used to describe such patients, including patients who
have had a high-quality evaluation with both endoscopy and a well-prepped
colonoscopy by an expert. When obscure bleeding is finally diagnosed, it is
usually found by endoscopy or colonoscopy, because lesions may be intermittent
or even lead to bleeding in the absence of an obvious break in the mucosa, as
occurs with Dieulafoy lesions. If endoscopy and colonoscopy results are
negative, techniques must be used that extend beyond the reach of these
standard procedures, including capsule endoscopy, push enteroscopy, or single
or double balloon enteroscopy. Radiographic tests that may be of value in the
evaluation of such patients include nuclear medicine bleeding scans, angiography,
and crosssectional i aging with computerized tomography (CT) scanning.
