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 μg tin per ml of blood to give the highest labeling yield. Using a new kit containing 2 μg 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.