[Non-erythrocyte 51Cr-activity--new results concerning an old labeling method (author's transl)]

Beside the yield of labeled erythrocytes the purity of the suspension of erythrocytes ready for injection from nonerythrocyte activity (NE51Cr) is an important criterion for the quality of the 51Cr-labeling method. After presentation of an especially precise method for measuring the NE51Cr the parameters influencing the NE51Cr in the main were investigated and the NE51Cr was analysed using different methods of separation of its components. ACD was used as anticoagulant. The results demonstrate that chromate-ions diffuse into the erythrocyte nearly completely in a very short time (max. 2.5 min). The incubation time (ICT: Time of the contact of erythrocyte and 51Cr) has an important influence in forming charged and/or neutral chromium (III)-citrate-complexes, which diffuse in part into the erythrocyte and lose the chromium ion inside the erythrocyte to other binding partners. The ion exchangeable anionic chromium-citrate-complexes preponderate in main against neutral and possibly existing cationic complexes. This part increases with increasing ICT. Only about the half of the complexes is protein bound (loosely in main), only a minimal part of the activity can be precipitated by ethanol. Using standard conditions in the Signette-method for rapidly 51Cr-labeling of erythrocytes with purification by an anionexchanger (ICT: 10 min) the NE51Cr is about 2.5%. The influence of varied conditions can be read form a nomogram. Reducing agents in the blood have some importance in extreme conditions, e. g. after 2.5 g L-ascorbic acid the NE51Cr is 5%. The in-vivo time course of two thirds of this activity shows a half time of more than 24 hours.