Biological Behavior of Erythrocytes Labeled In Vivo and In Vitro with Technetium-99m

Abstract

The in vitro method of red blood cell labeling was compared to the commonly used in vivo technique to evaluate labeling efficiency, levels of radioactivity in cells, plasma, and urinary excretion. Comparative studies were performed on nine normal volunteers. In two subjects, in vivo labeling did not occur. In the other subjects, the maximum blood activity (5 min after administration for the in vitro method and 15–120 min for the in vivo method) was 18% higher with the in vitro method (p < 0.005). Whole body retention of radioactivity was higher (78.7 ± 7.9%) with the in vivo method. With the in vitro method it was 66.3 ± 9.0% (p < 0.02).

It is concluded that the in vitro method of red cell labeling provides significantly higher blood levels of radioactivity at the times required for data collection but reduced whole body retention over 24 hr.