The Measurement of the Survival of Human Erythrocytes by In Vivo Tagging with Cr⁵¹

1. The deviation from a rectilinear form of the complex curvilinear curves of erythrocyte decay produced by the in vitro tagging of the cells with Na₂Cr⁵¹O₄ is not a result of the in vitro tagging procedure per se.

2. Human erythrocytes can be tagged its vivo with Na₂Cr⁵¹O₄. One can determine the in vivo survival of such cells if the gamma detecting unit is sufficiently sensitive and the amount of radiochromium used is sufficient. Such decay curves are similar to those produced by the in vitro Cr⁵¹ tagging method.

3. The in vivo method permits a study of the life span of erythrocytes in patients who have a very active cold agglutinin or in whom the cells are easily hemolyzed by mechanical trauma.