Deformability of Red Blood Cells and Correlation with ATP Content during Storage as Leukocyte-Depleted Whole Blood

Background: Storage duration of red cells has been associated with increased morbidity and mortality following transfusion. This association has been attributed to the loss of deformability of stored red cells leading to deterioration of microvascular perfusion. ATP content is considered a critical determinant of the deformability of stored red cells. Methods: ATP content and deformability were determined after storage for up to 49 days in 40 leukocyte-depleted whole blood units. Red cell deformability was determined using a laser-assisted optical rotational cell analyzer (LORCA (R)) employing shear stress (SS) ranging from 0.3 to 30 Pa. Deformability was expressed as the elongation index (EI). EI was correlated with ATP content. Results: ATP content decreased from 3.5 to 1.7 mu mol/g hemoglobin. EI increased from 0.03 to 0.05 at an SS of 0.3 Pa, and decreased from 0.62 to 0.59 at an SS of 30 Pa. Correlation coefficient (r) of ATP vs. EI at 0.3 Pa ranged from -0.17 to +0.15 during storage. At 30 Pa, r ranged from -0.03 to +0.45. Correlation increased with storage irrespective of SS, and increased with SS irrespective of storage. Conclusions: ATP content is not a valid surrogate marker for red cell deformability and may not reflect in vivo survival of stored red cells.