The first method involves removing blood from a vein.
The red blood cells are separated from the rest of the blood sample and then mixed with the radioactive material. The cells with the radioactive material are considered "tagged."
A short time later the tagged RBCs are injected into one of your veins.
The second method involves an injection of medicine.
The medicine allows the radioactive material to attach to your red blood cells.
The radioactive material is injected into a vein 15 or 20 minutes after you receive this medicine.
Scanning may be done right away or after a delay. For the scan, you will lie on a table under a special camera. The camera detects the location and amount of radiation given off by the tagged cells.
A series of scans may be done. The specific areas scanned depend on the reason for the test.
How to prepare for the test
You will need to sign a consent form. You put on a hospital gown and take off jewelry or metallic objects before the scan.
How the test will feel
You may feel a little pain when the needle is inserted to draw blood or to give the injection. Afterward, there may be some throbbing.
The x-rays and radioactive material are painless. Some people may have discomfort from lying on the hard table.
Why the test is performed
This test is most often done to find the site of bleeding in patients who have blood loss from the colon or other parts of the gastrointestinal tract.
Asimilar test called a ventriculogram may be done to check heart function.
A normal exam shows no rapid bleeding from the gastrointestinal tract.
What abnormal results mean
Your health care provider will determine the meaning of abnormalities on the scan.
What the risks are
Veins and arteries vary in size. Getting a blood sample from some people may be than from others.
Other slight risks from having blood drawn include:
Too much bleeding
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Very rarely, a person may have an allergic reaction to the radioisotope. This may include anaphylaxis if the person is very sensitive to the substance.
There is a small exposure to radiation from the radioisotope. There is very little radiation the materials break down so they are not radioactive in a very short time. Almost all radioactivity is gone in about 12 hours. There are no known cases of injury from exposure to radioisotopes. The scanner only detects radiation -- it does not give off radiation.
Most nuclear scans (including an RBC scan) are not recommended for women who are pregnant or breastfeeding.
Scans may need to be repeated over 1 or 2 days to detect gastrointestinal bleeding.
Segerman D, Miles KA. Radionuclide imaging: general principles. In: Adam A, Dixon AK, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 7.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.