Leukocyte scan

Alternative names 
WBC (nuclear) scan

Definition
A leukocyte scan is a nuclear scan (radioisotope test) using white blood cells (WBCs) that are “tagged” with radioactive material to locate areas of infection or inflammation.

How the test is performed
Nuclear WBC scanning uses small amounts of radioactive materials (radioisotopes) that are attached to a sample of white blood cells. These “tagged” white cells are returned to the body, and accumulate in areas of inflammation or infection (such as an abscess). The radiation emitted can be detected by a scanner, revealing hidden sites of infection or inflammation.

One or two vials of blood are withdrawn from a vein. The white blood cells are separated from the rest of the blood sample and are mixed with a small amount of a radioisotope (indium-111). About 2 or 3 hours later, these “tagged” white blood cells are returned to the body through injection into a vein.

Six and/or 24 hours later, the body is scanned. You are asked to lie on a table. The scanner looks similar to an X-ray machine, and detects radiation that is emitted from within the body by the radioactive white blood cells. It converts the detected radiation into an image that can be viewed on a screen or recorded on film. The scan takes about 1 or 2 hours. The scanner is usually located in a hospital, but often the test can be performed on an outpatient basis.

After the test is completed, no recovery time or special precautions are necessary. You typically may resume a normal diet, activity, and medications.

How to prepare for the test
There is usually no need for fasting, special diets, or preliminary medications. You must sign a consent form. You will wear a hospital gown or be allowed to wear loose fitting clothing without metal fasteners. Remove jewelry, dentures, or metal before the scan.

The health care provider will occasionally request that antibiotics be stopped before this test.

For infants and children:
The preparation you can provide for this test depends on your child’s ageand experience. For specific information regarding how you can prepare your child, see the following topics:

How the test will feel
There is a sharp prick from the needle during blood sampling and again when the blood is returned to you. The scan itself is painless, although the table that you are asked to lie on may be hard or cold. You do not feel the radioactive material.

Why the test is performed
WBC scan is most often performed when the health care provider suspects a hidden infection. It is particularly useful for suspected infection or inflammation within the abdomen. This test may be advised when there is suspected pyelonephritis, abscess, or osteomyelitis. It also may be advised when there is an unexplained fever (particularly after surgery).

Normal Values
A normal result is no localized accumulations of radioisotope-tagged WBCs (except for a certain amount in the liver and spleen, which normally accumulate white blood cells).

What abnormal results mean
Abnormal results will show accumulations of radioisotope-tagged WBCs, usually indicating an area of active inflammation or infection, such as a liver abscess or abdominal abscess.

What the risks are
The risks are essentially the same risks as for X-rays (radiation) and blood tests or intravenous injections.

There is a very slight exposure to radiation from the radioisotope. The spleen normally receives the highest dose of radiation because white blood cells normally accumulate in the spleen. The radiation from these materials is very slight, and the materials “decompose” (become no longer radioactive) in a very short time. Virtually all radioactivity is gone within 1 or 2 days. There are no documented cases of injury from exposure to radioisotopes. The scanner only detects radiation - it does not emit any radiation.

However, because of the slight radiation exposure, most nuclear scans (including WBC scan) are not recommended for women who are pregnant or breastfeeding (the radioisotope may be excreted in breast milk).

There is a minor risk that occurs whenever the body is penetrated (such as during blood sampling or injection of materials). This risk mainly involves the chance for infection or bleeding from the site. The risk for a WBC scan is no greater than when blood is sampled or material is injected into a vein for other reasons.

Extremely rarely, a person may experience an allergic reaction to the radioisotope. This may include anaphylaxis if the person is extremely sensitive to the substance.

Special considerations
The long delay before the person can be scanned may be undesirable for critically ill people.

Other tests (such as CT scan or ultrasound) may be required to confirm the presence of inflammation or infection indicated by an abnormal WBC scan.

False-negative results can theoretically occur as a consequence of antibiotic usage or chronic infection. Infection in the liver or spleen can be missed because of normal WBC accumulation in these organs.

False-positive results can occur from many causes, including (but not limited to) bleeding, the presence of tubes or catheters in the body, and skin wounds (such as surgical incisions). WBC accumulations in the lungs does not necessarily indicate an infection in the lungs.

Johns Hopkins patient information

Last revised: December 8, 2012
by Brenda A. Kuper, M.D.

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