Definition

GI bleeding studies uses radioactive materials in the investigation of bleeding from the gastrointestinal (GI) tract. These studies go under various names such as "GI bleeding scans" or "Tagged red blood cell scans." They are performed and interpreted by radiologists (physicians who specialize in diagnosis and treatment of diseases by means of x rays or related substances).

  Purpose

These studies are designed to find the source of blood loss from the GI tract; that is the stomach, small bowel, or colon. They work best when bleeding is either too slow, intermittent, or too rapid to be identified by other means, such as endoscopy, upper GI series, or barium enema.

They are particularly useful when other methods have not been able to determine the site or cause of bleeding.

  Precautions

Because of the use of radioactive materials, these studies are best avoided in pregnant patients. Another important relates to the interpretation of these tests, whether normal or abnormal. Since these studies are far from perfect, they can only be used as "guides" as to the cause or site of bleeding. In most instances, further studies must be performed to confirm their findings.

  Description

Bleeding scans are based on the accumulation of radioactive material as it exits from the vessels during a bleeding episode. Blood is first withdrawn from the patient. Then, the blood, along with a radioactive substance is injected into a vein and over several hours scans measuring radioactivity are performed. The studies were initially reported to be very sensitive and accurate; however, critical evaluation of these tests have shown them to be less accurate than originally believed.

  Preparation

No preparation is needed for these tests. They are often done on an "emergency" basis.

  Aftercare

No special care is needed after the exam.

  Risks

Bleeding scans are free of any risks or side-effects, aside from the fact that they should best be avoided in pregnancy.

Normal results

A normal exam would fail to show any evidence of accumulation of radioactive material on the scan. However, scans may be normal in as many as 70% of patients who later turn out to have significant causes of bleeding. This is known as a false-negative result. A patient must be bleeding at the same time the scan is performed for it to be seen. Therefore, not finding evidence of a bleeding source during the study, can be misleading.

Abnormal results

The accumulation of radioactive material indicating a "leakage" of blood from the vessels is abnormal. The scan gives a rough, though not exact, guide as to the location of the bleeding. It can tell where the bleeding may be, but usually not the cause. Thus, extreme caution and skill is needed in interpreting these scans, and decisions involving surgery or other treatment should await more definitive tests.

   Key Terms:

Endoscope, Endoscopy An endoscope as used in the field of gastroenterology is a thin flexible tube which uses a lens or miniature camera to view various areas of the gastrointestinal tract. The performance of an exam using an endoscope is referred by the general term endoscopy. Diagnosis through biopsies or other means and therapeutic procedures can be done with these instruments.

   Resources:

Books

• Lane, Loren. "Radionuclide Scanning." In Sleisenger & Fordtran's Gastrointestinal and Liver Disease, ed. Mark Feldman, et al. Philadelphia: W. B. Saunders Co., 1997.

Periodicals

• Mujica, Victor R. and Barkin, Jamie S. "Occult Gastrointestinal Bleeding." Gastrointestinal Endoscopy Clinics of North America (Oct. 1996): 833-845
• Shapiro, Marcelle J. "Radionuclide Scans." Gastroenterology Clinics of North America (Mar. 1994): 125-128