Technetium-99m labeling of red blood cells: in vitro evaluation of a new approach

By titration of two different stannous kits for 99mTc labeling of red blood cells (RBC) we found concentrations of 1-2 micrograms tin per ml of blood to give the highest labeling yield. Using a new kit containing 2 micrograms of tin and 0.1% hypochlorite (NaOCl) as an oxidizing agent we labeled RBC with 99mTc avoiding centrifugation of cells. To evaluate this new procedure we assessed the dependency of tin incubation time, and addition of 4.4% EDTA as a chelating agent on labeling efficiency. We also measured the dependency of EDTA on the stability of the label. Optimal conditions for labeling of 1 ml of whole blood using the new stannous kit were: 5-10 min of tin incubation, 0.2 ml of 0.1% hypochlorite, and 15 min of 99mTc incubation. This procedure resulted in a labeling efficiency of at least 96%. The overall effect of EDTA was not an increased labeling efficiency, and EDTA increased the stability of the label with only a few percent. The promising results of this new labeling approach encourage to further laboratory investigations and eventual clinical evaluation of the procedure.