Red cell cryopreservation for serologic testing: bulk freezing with polyvinylpyrrolidone (PVP)

Background/aim: Red cell cryopreservation is essential for immunohematology reference laboratories. Various cryopreservation methods maintain the structural integrity of red cells, such as bulk freezing with glycerol and droplet freezing with polyvinylpyrrolidone (PVP). In this paper, we provide a technical note with real-world data and report our experience with a modified PVP bulk-freezing method in a transfusion medicine setting. Materials and methods: Red cells were separated from whole blood samples and incubated for 1 h at room temperature with PVP with slow agitation or no agitation before freezing. Instead of using the established method of shock freezing droplets in liquid nitrogen, the red cells were frozen as 1 mL bulk samples. Recovery rates were determined for different thawing temperatures. Results: The overall red cell recovery rate was 45%±9% (mean±standard deviation). The recovery rates were 42.3%±8.1% in samples incubated without agitation (n = 27) and 47.9%±9.3% with slow agitation (n = 24) before freezing (p = 0.017). The recovery rates at different thawing temperatures, were 34.0%±2.0% at 22 °C, 46.6%±9.3% at 37 °C, and 40.8%±4.9% at 42°C (p=0.007). A generalized linear model confirmed that slow agitation during incubation yielded higher recovery than no agitation (p = 0.029). Conclusion: Bulk freezing of red cells with PVP in liquid nitrogen yielded 45% recovery. Our modified method may be preferred for cryopreservation and storage of large volumes. Bulk freezing with PVP can be particularly useful in applications where maximizing storage efficiency is more important than minimizing cell loss.