LABELED WBC STUDY

INDICATIONS:

1. Evaluation of inflammatory bowel disease.
2. Detection of abscess or acute (<4-6 weeks) infection.
3. Fever of unknown origin.
4. Acute osteomyelitis (particularly useful in diabetics).
5. Prosthesis infection, graft infections.

PATIENT PREPARATION:

No special preparation required. For patients with inflammatory bowel disease, no barium should be in the GI system. Check patient's CBC for severe leukopenia.

RADIOPHARMACEUTICAL:

Indium-111 (400-750 mCi) or 20 mCi of Tc-99m labeled leukocytes are injected I.V. The critical organ is the spleen which receives 2-18 rad depending on the isotope used.

SCANNING TIME:

Blood is withdrawn from the patient and the white blood cells are labeled with In-111-oxine or Tc-99m-HMPAO and then re-injected. The separation of white blood cells and their labeling requires approximately 3 hrs. The patient returns for imaging at 1.5, 3.0 or 24 hours after injection. Scan time is approximately 30 minutes depending on site of interest.

OTHER CONSIDERATIONS:

1. This study is most sensitive for acute infections (<4-6 weeks duration). Sensitivity also declines with antibiotic therapy, but this will not preclude doing the exam.
2. The spleen receives a relatively high dose of radiation. This should be kept in mind when repeat Indium scans are considered in a patient.
3. Compared with Ga-67, labeled WBCs has less interference from GI, tumor, and normal soft tissue activity. The radiation dose to the spleen, however, is higher with Indium.

RATIONALE

Isotope chelated to oxine is lipophilic and diffuses across leukocyte cell membranes. Once inside, In-111/Tc99m04 is retained by the cell while leukocyte function is preserved. This enables the nuclear physician to image the concentration of labeled leukocytes in response to inflammatory processes.