[Techniques for estimating red cell life span and its interpretation].

The measurement of red cell life span can be very useful in the study of various hemolytic diseases. The classical method for the measurement of red cell life span was the transfusion of compatible but immunologically identifiable cells. In recent years, it has been completely replaced by techniques based on radioisotope labeled red cells. Direct methods for estimating red cell life span can be divided into two categories; one that labels a cohort of cells and the other that labels cells randomly. Cohort methods depend on the incorporation of isotopically labeled substances into a group of newly produced red cells. Random label methods involve the use of isotopes that bind to red cells of any age in the circulation. The patterns of time dependent change in labeled circulating red cells produced by these two methods differ. Cohort labels are characterized by a pattern with a plateau, the length of which is an estimate of red cell life span. In contrast, random labels begin to decrease from the circulation instantly, and red cell life span is related to the time required for the label to fade completely. Random label methods are more useful than cohort methods for clinical applications. The chromium method is used more frequently than any other available method in Japan.