Optimization and evaluation of the in vitro method for labeling RBC in whole blood with Tc-99m

This study was undertaken to establish optimum conditions for the selective labeling of RBC in whole blood with Tc-99m, and to evaluate the in-vivo behavior of the labeled RBC. Effect on Tc-99m labeling of parameters such as the chemical form and the content of tin in the kits, uptake kinetics, the role of oxidants and chelating agents for the removal of extracellular tin, volume effects, etc., were investigated using Sn-117m or Sn-113 labeled kits. Out of the several ligands studies, citrate and glucoheptonate were found to be most effective for transporting tin into the cells. Stannous citrate kits containing 2, 15 and 50 ..mu..g tin were selected for further studies. The tin uptake into RBC was found to increase in proportion to the blood volume, tin content of kits and incubation times. The uptake was fastest within the first 10 min and then it increased very slowly up to 2 hr. The uptake of Tc-99m was dependent only on the extracellular tin (II); intracellular tin content was important only when carrier levels of Tc-99 were present. The final procedure was: (I) incubation of 1-4 ml blood with 50 ..mu..g tin (Sn/sup 2+/ citrate) kits for 5 min; (II) addition withmore » mixing of 0.6 ml 0.1% NaOCl followed by 1.0 ml 4.4% disodium EDTA; and (III) addition of the desired amount of /sup 99m/TcO/sub 4//sup -/ and incubation for 15 min. Labeling yields were consistently >95%. Studies in dogs demonstrated that the in vivo survival of the label in blood was equal to or somewhat superior than that when using other labeling techniques. In a study in human volunteers (n=16) excellent images of the blood pool were obtained. At 45 min after injection, 97% activity remained intravascular and 94% of this was associated with the RBC.« less