Observations on the Chromium Labelling of ACD‐Stored and Previously Frozen Red Cells

Chromium labelling characteristics of both ACD‐stored and previously frozen red cells were evaluated. The chromium uptake of previously frozen red cells processed by agglomeration was inversely related to the hemoglobin level of the suspending fluid. Ascorbic acid was not needed for the labelling of previously frozen, agglomerated red cells. Cellular injury, as measured by increase in supernatant hemoglobin during post‐thaw storage at 4 C, occurred with the agglomerated, previously frozen red cells when: (1) Na2 EDTA was present in the glycerolizing solution; (2) the disaggregation of the agglomerated red cell mass was carried out with 75 rather than 250 ml of isotonic saline; and (3) the storage temperature of the glycerolized red cells was interrupted for one week with a storage interim at either 4 C or −20 C. By use of a phthalate ester technic, red cells were separated into three fractions on the basis of cellular density. Preferential chromium labelling of red cells was noted: the lightest fraction contained significantly more radioactivity than the heaviest fraction.