White cell scan
White cell scan is used for the assessment of the disease extent and activity in Crohn’s disease.
How is the white cell scan performed?
- A blood sample is obtained from the patient. The leucocytes are separted from erythrocytes and platelets. Leucocytes labelling is achieved by incubation with the radioisotope in plasma or saline. The radioisotopes used are either Indium-111 tropolonate (111 In) or Technetium-99m hexamethyl propylene amine oxime (99m Tc HMPAO). This process takes a couple of hours (thus the patient is asked to return after a couple of hours). Results from 99m Tc HMPAO in small bowel disease are better than those obtained from 111 In
- The tagged white cells are injected intravenously in the patient. After injection, the labelled white cells migrate into the inflammed lesion before being shed into the bowel lumen.
- Images are obtained with a gamma camera at 2-6 hrs later. A late image (24 hrs) may be required if the technique is used to detect infection.
What are the disadvantages of the white cell scan?
- False negative scans. However, this is rarely seen in symptomatic patients with active disease. A negative scan in a symptomatic patient virtually excludes Crohn’s disease.
- Useful only for active disease
- Difficulty in identifying the various bowel segments
