A trial study of leukocyte labeling with stabilized Tc-99m D,L-HMPAO by methylene blue and sodium phosphate buffer

We attempted to label leukocytes with stabilized Tc-99m D,L-HMPAO by methylene blue and sodium phosphate buffer (S-HMPAO). Methods: The results were compared with unstabilized Tc-99m D,L-HMPAO (U-HMPAO). U-HMPAO was obtained by reconstituting a commercial vial of D,L-HMPAO. Stabilization of the kit was performed by the addition of methylene blue. The leukocytes were labeled using a modified published method. The test samples of S-HMPAO and U- HMPAO were prepared immediately, and stood for 0.5, 1, 2, 4, and 6 h, respectively, at room temperature before analysis. Results: In comparison with U-HMPAO: (1) the radiochemical purity of S-HMPAO was higher; (2) the labeling efficiencies of S-HMPAO labeled leukocytes were higher and consistent; (3) the viability of S-HMPAO labeled leukocytes was as high as the viability of U-HMPAO labeled leukocytes at any time; and (4) the percentages of disintegrated from S-HMPAO labeled leukocytes in plasma were lower. Conclusion: S-HMPAO is more stable than U-HMPAO and can provide higher leukocyte labeling efficiency. S-HMPAO, therefore, has the potential to replace U-HMPAO as a leukocyte-labeling agent.