A simple in vitro method of radiolabelling human erythrocytes in whole blood with 113mIn-tropolonate.

A simple and rapid in vitro procedure has been developed for selectively radiolabelling erythrocytes in whole blood using 113mIn-tropolonate. A maximum labelling efficiency of 97% was achieved, of which 95.5% was on the erythrocytes after only 5 min incubation of whole blood at room temperature. The optimum amount of tropolone for labelling whole blood was 10 micrograms of tropolone per ml of blood using acid-citrate dextrose (ACD) as the anticoagulant and 50 micrograms of tropolone per ml of blood using heparin. Under these optimum conditions, only 2.5% of the cell-bound 113mIn was released from the labelled cells during a 1 h in vitro incubation in cell-free plasma, irrespective of the anticoagulant used. These results suggest that 113mIn-tropolonate may prove to be a useful in vitro agent for labelling erythrocytes for short-term clinical investigations, especially at centres where 99mTc and 111In are unavailable.