A tagged white blood cell (WBC) scan is a nuclear medicine study used to diagnose and localize areas of infection and/or inflammation. It can be helpful when an occult infection such as pyelonephritis, abdominal abscess or osteomyelitis is suspected. A major component of the immune system’s defense mechanism is the activation and upregulation of white blood cells. These cells can be found in large numbers in areas where there is active inflammation and/or infection; the ability to “tag” these cells allows the detection of such foci in the evaluation of patients with a suspected source of infection.

To perform a tagged WBC scan, a sample of the patient’s WBCs is mixed with the radioactive material indium oxine, isotype 111 (¹¹¹In). The tagged sample is then reinfused intravenously to the patient. If there is an area of active inflammation/infection, a scanner will detect localized areas of these tagged white cells and convert them into an image viewed on a screen or recorded on film. The scan takes approximately 1 to 2 hours and requires patient transport to the nuclear medicine suite.

There are several special considerations when deciding whether a tagged WBC scan is the appropriate diagnostic tool. False-negative results can occur due to antibiotic use or chronic infection, and because WBCs are usually found in the spleen and liver, a true infection in these organs can be missed with the scan. False-positive results can occur due to bleeding and the presence of tubes, drains, or catheters in the body. Because the patient has to wait 6 to 24 hours to be scanned after the reinfusion, this study may not always be the best option for the critically ill patient.