GI Consult: Occult and Obscure Gastrointestinal Bleeding

Even though a variety of diagnostic procedures are available, narrowing down the many potential causes of gastrontestinal bleeding may be a lengthy process. It may not even be possible in all patients.

By Andrew Black, MD, and Charles Maltz, MD

1. What is the difference between occult gastrointestinal bleeding and obscure gastrointestinal bleeding?

Occult gastrointestinal bleeding is indicated by positive results of a fecal occult blood test or the indication of iron deficiency anemia, both in the absence of obvious evidence of bleeding. Obscure gastrointestinal bleeding refers to prolonged or recurrent bleeding of uncertain origin as manifested by iron deficiency anemia or visible bleeding or as confirmed by positive results of a fecal occult blood test. The labeling of gastrointestinal bleeding as obscure indicates that the cause of the bleeding has not been determined after an initial gastrointestinal evaluation.

2. What is the "standard" initial evaluation of gastrointestinal blood loss?

Colonoscopy and upper endoscopy are the first tests for elucidating the cause of both obscure and occult blood loss. However, even after both examinations are performed, the cause of blood loss may not be identified in a number of patients. After repeated colonoscopy and upper endoscopy, the portion of undiagnosed cases will decrease to about 5%.

3. Why repeat the colonoscopy or upper endoscopy?

Although endoscopy is an excellent test to determine the source of gastrointestinal bleeding, like any other test, it is not 100% sensitive. A spastic duodenal bulb may make a small duodenal ulcer difficult to identify. Occasionally a small ulcer located in a large hiatal hernia (Cameron's ulcer) may be overlooked. A vascular ectasia in a less than optimally prepared colon can easily be missed. In addition, on occasion large polyps or even cancer of the colon may escape detection.

4. What should be done if the origin of occult bleeding is not discovered via colonoscopy or upper endoscopy?

Most cases of occult bleeding in which the origin is not firmly identified do not eventually result in obscure bleeding. In many cases the bleeding simply stops without the source ever being identified. Therefore, in the evaluation of most cases of occult bleeding, diagnostic testing other than colonoscopy and upper endoscopy may not be necessary, even in the absence of positive results from these tests. However, further investigation is warranted when persistent bleeding necessitates repeated transfusions.

5. What diagnostic studies should be undertaken in the case of recurrent or persistent iron deficiency anemia in the presence of negative results from colonoscopy and upper endoscopy? 

In the patient who has anemia but no positive results documented by the Hemoccult stool test, appropriate studies should be undertaken to determine that the anemia is indeed caused by gastrointestinal blood loss. Iron deficiency anemia may be caused by chronic urinary bleeding or by heavy perimenopausal bleeding. Patients with thalassemia minor will have hypochromic/microtic red cells and a hemoglobin reading approximately 15% below normal. In addition, iron deficiency may be the sole symptom of celiac sprue.

If celiac disease is suspected, a small bowel biopsy can be performed at the time of upper endoscopy. If gastrointestinal blood loss is suspected to be the cause of the iron deficiency anemia, additional Hemoccult testing should be performed.

6. How does one proceed when a patient has periodic episodes of frank gastrointestinal bleeding but neither colonoscopy nor gastroscopy can identify the lesion?

At this point the difficult task of evaluating the small bowel for a bleeding site begins. The two endoscopic techniques used to evaluate the small bowel are push enteroscopy and Sonde endoscopy. Push enteroscopy involves the use of a special enteroscope of increased length, which in experienced hands can be advanced as much as 100 cm past the ligament of Treitz.

In Sonde enteroscopy, a tube is passed either through the nose or the mouth and is advanced by peristalsis into the small intestine. Sonde enteroscopy is a lengthy and uncomfortable procedure, however. In evaluating the small bowel one should not forget that the terminal ileum can usually be visualized at colonoscopy by intubating the ileum when the colonoscope is in the cecum.

A Meckel scan is a radionuclide imaging method that is used to visualize a Meckel diverticulum, which is a diverticulum of the small bowel that contains gastric mucosa and is at risk for ulceration.

In rare cases of continued bleeding from a suspected small bowel source, intraoperative enteroscopy has been performed. In this technique, an enteroscope is passed orally as far as possible into the small bowel. With the scope in place, a laparotomy—or laparoscopy—is performed and the scope is advanced further into the small bowel by the surgeon, who pleats the small bowel onto the scope.

7. Is there any role for radiologic studies in the evaluation of obscure gastrointestinal bleeding?

The traditional small bowel series is often performed to evaluate gastrointestinal bleeding, as is enteroclysis, the instillation of barium directly into the small bowel via a tube that has been passed nasally into the small bowel. Enteroclysis is relatively accurate in detecting small bowel tumors or Crohn's disease but is of limited use in diagnosing vascular ectasia. A labeled red blood cell scan can detect bleeding if the rate is between 0.1 and 0.4 mL/min. Unfortunately, the high false-positive rate of such scans makes this technique less than ideal. If the rate of bleeding is greater than 0.5 mL/min, angiography may yield diagnostic clues to the cause. In addition, the vascular pattern on angiography may suggest the presence of a lesion.

8. I read recently about a small camera that transmits images of the small bowel after the device is swallowed. Is there really such a device?

Yes, and it is currently undergoing clinical testing. The patient swallows a small capsule that has a self-contained light source as well as a transmitter. The capsule is allowed to pass through the gastrointestinal tract by normal peristalsis and eventually passes in the stool. The data (images of the small bowel mucosa) are collected by and contained in the receiver, which is worn about the waist while the capsule is traversing the small bowel. The data in the receiver are then analyzed by a special proprietary computer program, which can indicate images that show suspicious lesions and their location within the small bowel. The images can then be examined by a gastroenterologist.

9. What are the most common types of lesions found in patients whose fecal occult blood test results are positive?

In approximately 25% of patients who have positive results of Hemoccult testing, endoscopic evaluation reveals a colonic source for the bleeding. In a slightly higher percentage, an upper gastrointestinal source is responsible. The colonic sources include neoplasia, such as cancer or large polyps, whereas the upper sources are often peptic ulcers or reflux esophagitis. Vascular ectasia have been found in both the upper and lower gastrointestinal tracts. In addition, use of nonsteroidal antiinflammatory drugs can cause erosions in both the stomach and the small and large intestines.

10. What are the most common causes of obscure gastrointestinal bleeding?

A small bowel bleeding source is the most common cause of obscure gastrointestinal bleeding in those patients for whom results of repeated upper and lower endoscopic procedures have been normal. The patient's age is helpful in identifying the most likely cause of obscure gastrointestinal bleeding. In patients older than 60 years of age, vascular ectasia is the most common culprit. In younger patients small bowel tumors are often the cause.

11. What treatments are available once a bleeding source is identified?

The treatments range from surgery for neoplasia to endoscopic therapy for ectasia to medical therapy for peptic ulcers and esophagitis. Some patients with persistent obscure bleeding respond to treatment with a combination of estrogen and progesterone. Although it is not the ideal therapeutic option, sometimes periodic transfusions and iron supplementation are all that can be done to treat obscure gastrointestinal bleeding.

12. Evaluation of obscure gastrointestinal bleeding sounds like a lengthy as well as costly process.

Thorough examination may necessitate multiple endoscopic procedures and sometimes hospitalization. Even then, the source of the bleeding may never be identified in a significant number of patients, and such patients would then have to undergo empirical treatment.