Stabilized with Methylene Blue

The in vitro viability, chemotaxis, and labeling stability of leukocytes labeled using 99mTc-exametazime stabilized with methylene blue were evaluated and compared with those obtained using nonstabilized 99mTc-exametazime. Methods: Two identical leukocyte populations, from 30 healthy donors, were labeled simultaneously using freshly prepared and 2-h-old stabilized 99mTc-exametazime. The following quality control techniques were performed on each labeled leukocyte sample: eosin Y staining, chemotaxis radioassay, and labeling stability at 2 h after labeling. Results: Eosin Y staining showed a cell viability of at least 98% in all samples, without a significant statistical difference between the populations. Chemotactic indices obtained with leukocytes labeled with freshly prepared, unstabilized 99mTc-exametazime were statistically greater than those obtained using 99mTc-exametazime stabilized with methylene blue ( z 5 2.41; P , 0.02). Labeling stability at 2 h after labeling was the same for both populations. Conclusion: The use of 99mTc-exametazime stabilized with methylene blue for leukocyte radiolabeling does not affect either cell membrane integrity or labeling stability but can cause a decrease in the cell chemotactic capacity that discourages its clinical use.