Red Cell Cryopreservation For Serologic Testing: Bulk Freezing With Polyvinyl Pyrrolidone (Pvp): Technical Note

<strong>Background/aim</strong>. Red cell cryopreservation is an essential tool in immunohematology reference laboratories. 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.

<strong>Materials and methods. </strong>Red cells were separated from whole blood samples and incubated for 1 hour at room temperature with PVP using slow agitation or no 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. Recovery rates were determined for different thawing temperatures.

<strong>Results</strong>. 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, depending on the 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).

<strong>Conclusion.</strong> Bulk freezing of red cells with PVP in liquid nitrogen allowed a recovery of 45%. 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.