Background/Case Studies: Red cell cryopreservation is an essential tool in immunohematology reference laboratories. Samples of red cells with rare blood group antigens are stored at -80 °C or in liquid nitrogen for years. Various cryopreservation methods are widely applied to maintain the structural integrity of red cells, such as bulk freezing with glycerol or droplet freezing with polyvinyl pyrrolidone (PVP). Here, we provide a technical note with real-world data and report our experience from a transfusion medicine setting using bulk freezing with PVP, as a method modification.
Study
Design/Methods: Whole blood samples of the 48 patients were collected and shipped internationally. Red cells were separated and incubated for 1 hour at room temperature with PVP with slow agitation or without agitation before freezing. In difference to the established shock freezing as droplets in liquid nitrogen, the red cells were frozen as 1 mL bulk samples in vials. Recovery rates were determined for different thawing temperatures.
Results/Findings: The overall red cell recovery rate was 60% ± 10% (mean ± standard deviation). The recovery rate was 56.3% ± 10.5% in samples incubated without agitation (n=26), and 62.7% ± 9.9% in the samples incubated with slow agitation (n=25) before freezing (p=0.019). The recovery rates, depending on the thawing temperatures, were 50.7% ± 7.1% at 22 °C, 61.2% ± 11.0% at 37 °C, and 54.1% ± 6.7% at 42 °C (p=0.050). A generalized linear model confirmed thatthawing temperature and incubation method influenced the red cell recovery outcomes (p=0.029).
Conclusions: Bulk freezing of red cells with PVP in liquid nitrogen allowed a recovery of more than 60%. Our modified method may be preferred for cryopreservation when large volumes of red cells need to be stored. Bulk freezing with PVP can be particularly useful in applications where maximizing storage efficiency is more important than minimizing cell loss.
