A white blood cell (WBC) scan is an imaging test that uses a radioactive substance (called a tracer) to look for areas of infection or inflammation in the body.

See also: Nuclear scan

Blood will be taken from one of your veins. White blood cells are separated from the rest of the blood sample and then mixed with a small amount of a radioactive material (radioisotope) called indium-111. The cells with the radioactive material are considered "tagged."

About 2 or 3 hours later, the tagged white blood cells are returned to your body through injection into a vein. The tagged cells gather in areas of inflammation or infection.

Approximately 6 to 24 hours later, your body is scanned. You lie on a table. The scanner looks like an x-ray machine. It detects the radiation given off by the radioactive white blood cells. A computer 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.

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.

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.

WBC scan is most often done when your doctor suspects a hidden infection. It is particularly useful for suspected infection or inflammation within the abdomen.

This test may be recommended if you have suspected pyelonephritis, abscess, osteomyelitis , or unexplained fever, particularly after surgery.

A normal result means there are no accumulations of tagged cells (except for a certain amount in the liver and spleen, which normally accumulate white blood cells).

Abnormal results usually suggest an active inflammation or infection, such as a liver abscess or abdominal abscess.

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.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

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.

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.

Segerman D, Miles KA. Radionuclide imaging: general principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 7.

Wilson DJ, Berendt AR. Bone and soft tissue infection. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 51.