Evaluation of a new leukocyte labeling procedure with ^99mTc-HMPAO

A technique for labeling leukocytes with ^99mTc using hexamethylpropylene-amineoxime (HMPAO) was evaluated in vitro. The labeling procedure resulted in a cell bound fraction of radioactivity of 56% after ^99mTc incubation and 96% after 1 washing of cells. In the final cell suspension 84% of the radioactivity was attached to the polymorphonuclear (PMN) leukocytes constituting 94% of white cells. Only 5% was bound to residual red blood cells. The stability evaluated in autologous plasma showed a decline of cell bound activity from 96% to 84% over 3 h. The chemotactic function of PMN leukocytes was unaffected by the labeling procedure. These findings demonstrate that HMPAO, albeit cell unspecific, is efficient for labeling PMN leukocytes with ^99mTc. The stability of the labeling procedure is high and the technique does not affect cell function. No other current ^99mTc leukocyte labeling technique possesses all these qualities.