What is a tagged White Blood Cell (WBC) scan?

From the Guidelines

A tagged white blood cell scan is recommended as a subsequent imaging study after initial cross-sectional imaging is inconclusive in determining the origin of sepsis, as it provides diagnostic information with high sensitivity and specificity, as seen in a study by Carter et al 1. When considering the use of a tagged white blood cell scan, it is essential to weigh the benefits and limitations of this imaging modality. The scan involves labeling a patient's white blood cells with a radioactive tracer, typically technetium-99m or indium-111, and then reinjecting them into the body. The tagged cells migrate to areas of infection or inflammation, which can be detected using a special camera.

Key Points to Consider

• The procedure typically takes 2-4 hours, with imaging occurring 24 hours after injection for optimal results.
• The scan is particularly useful for locating abscesses, osteomyelitis (bone infections), inflammatory bowel disease, and infections in prosthetic joints or implanted devices.
• It is valuable when other imaging techniques like CT or MRI are inconclusive.
• The radiation exposure is minimal and considered safe for most patients, though pregnant women should avoid this test.
• The scan works because white blood cells are the body's natural infection fighters, so they concentrate in areas where infection or inflammation is present, allowing doctors to precisely identify problem areas that might otherwise be difficult to locate.

Recent Studies and Guidelines

• A study published in the Journal of the American College of Radiology in 2024 found that radiolabeled WBC scans may be useful as a subsequent imaging study in providing diagnostic information when initial cross-sectional imaging is inconclusive in determining the origin of sepsis 1.
• Another study published in the European Journal of Nuclear Medicine and Molecular Imaging in 2010 discussed the guidelines for labeling leucocytes with 99mTc-HMPAO, highlighting the importance of using freshly prepared Tc-HMPAO for leucocyte labeling 1.
• A 2016 study published in Diabetes/Metabolism Research and Reviews discussed the use of nuclear medicine scans, including tagged white blood cell scans, in the diagnosis and management of foot infections in persons with diabetes 1.
• A 2023 study published in the Journal of the American College of Radiology discussed the use of WBC scans and sulfur colloid scans in the workup of suspected infection in knee arthroplasty, highlighting the potential benefits and limitations of these imaging modalities 1.

Recommendations

• A tagged white blood cell scan should be considered as a subsequent imaging study after initial cross-sectional imaging is inconclusive in determining the origin of sepsis.
• The scan should be used in conjunction with other imaging modalities, such as CT or MRI, to provide a comprehensive diagnosis.
• Patients with suspected infection or inflammation in prosthetic joints or implanted devices may benefit from a tagged white blood cell scan.
• Pregnant women should avoid this test due to the minimal radiation exposure.

From the Research

Tagged White Blood Cell Scan

• A tagged white blood cell scan is a diagnostic imaging test used to evaluate suspected infections, such as osteomyelitis, vascular access infections, and fever of unknown origin 2.
• The test involves labeling a patient's white blood cells with a radioactive tracer, such as indium-111 or technetium-99m, and then imaging the body to see where the labeled cells accumulate 3, 4.
• The clinical utility of tagged white blood cell scans varies by indication, with higher utility for suspected osteomyelitis and vascular access infections, and lower utility for evaluating fever of unknown origin 2.
• The sensitivity, specificity, and diagnostic accuracy of tagged white blood cell scans also vary, with reported values ranging from 84% to 98% sensitivity, 56% to 98% specificity, and 72% to 98% diagnostic accuracy 3, 4.

Diagnostic Performance

• Tagged white blood cell scintigraphy has been shown to have high diagnostic performance in detecting device-related infections, with a sensitivity of 94% and a negative predictive value of 95% 5.
• The test can also provide information on the extent of device involvement and detection of associated complications, such as infectious endocarditis and septic embolism 5.
• However, false-positive and false-negative results can occur, highlighting the need for careful interpretation of scan results and correlation with clinical findings and other diagnostic tests 6, 5.

Comparison with Other Diagnostic Tests

• Tagged white blood cell scans have been compared with other diagnostic tests, such as bone scans and echography, and have been shown to have advantages in terms of sensitivity and specificity 3, 5.
• However, the choice of diagnostic test depends on the specific clinical scenario and the availability of resources, and tagged white blood cell scans should be used in conjunction with other diagnostic tests and clinical evaluation to guide patient management 2, 5.