Chemotaxis, viability, and labeling stability of leukocytes labeled with Tc-99m-exametazime stabilized with methylene blue

The in vitro viability, chemotaxis, and labeling stability of leukocytes la beled using Tc-99m-exametazime stabilized with methylene blue were evaluate d and compared with those obtained using nonstabilized Tc-99m-exametazime. Methods: Two identical leukocyte populations, from 30 healthy donors, were labeled simultaneously using freshly prepared and 2-h-old stabilized Tc-99m -exametazime. The following quality control techniques were performed on ea ch labeled leukocyte sample: eosin Y staining, chemotaxis radioassay, and l abeling stability at 2 h after labeling. Results: Eosin Y staining showed a cell viability of at least 98% in all samples, without a significant stati stical difference between the populations. Chemotactic indices obtained wit h leukocytes labeled with freshly prepared, unstabilized Tc-99m-exametazime were statistically greater than those obtained using Tc-99m-exametazime st abilized with methylene blue (z = 2.41; P < 0.02). Labeling stability at 2 h after labeling was the same for both populations. Conclusion: The use of Tc-99m-exametazime stabilized with methylene blue for leukocyte radiolabeli ng 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.