The metric for characterizing optimal centrifugation is percent plasma recovery. Converting plasma volume into a percent standardizes plasma yields and reduces variability associated with donor and process differences.
This section will review TCF calculations and demonstrate how different centrifugation protocols may achieve the same TCF with equivalent plasma recovery. Defining TCF for a centrifugation protocol is the key to achieving optimal plasma yields.
Total Centrifugal Force (TCF)
Determining centrifuge parameters is often a choice of whether to spin blood at faster speeds (or RCF) for shorter timed intervals or at lower speeds for longer timed intervals. However, to optimize centrifugation it is more important to select the appropriate TCF for your process. Figure 3 illustrates centrifuge profiles comparing centrifugation at 5000 rpm (7284 g) for 7 minutes versus 4150 rpm (5000g) for 10 minutes. When the area under the curve is calculated, the TCF for each condition is the same (approximately 2.5 x 106 g•s). Therefore, centrifugation at a higher g force for shorter time produces the same TCF as spinning at a lower g force for a longer time.
Centrifuge Profile with Equivalent TCF
How does this relate to total plasma recovery? Many believe that spinning at higher RPM is critical for recovering the maximum volume of plasma. Figure 4 and Table 3 represent the same data in a different format and confirm that regardless of whether using higher RPM for shorter spin times (orange curve) or lower RPM for longer spin times (green curve), the percent plasma recovery is dependent on the total centrifugal force or TCF. Therefore, Total Centrifugal Force is the key to optimizing centrifugation processes.
TCF for Differing RPM Settings and % Plasma Recovery
Equivalent % Plasma Recovery at Comparable TCF
|1.09 x 106
||5000 rpm 4 min
|1.11 x 106
||4150 rpm 5 min
|1.72 x 106
||4150 rpm 7 min
|2.02 x 106
||5000 rpm 6 min
|2.42 x 106
||5000 rpm 7 min
|2.65 x 106
||4150 rpm 10 min
|3.71 x 106
||5000 rpm 10 min
|4.11 x 106
||4150 rpm 15 min
Understanding TCF can be invaluable when trying to compare the results from more than one spin condition or when trying to obtain the same results at various facilities using different centrifuge settings or centrifuges.
The impact of deceleration on sedimentation is perceived to be negligible. However brake setting can significantly impact the red cell plasma interface and should be considered when centrifuge optimization is performed.
The data in Figure 5 show that maximum brake settings disrupt the red cell plasma interface at lower TCF but not significantly at higher TCF.
One-way ANOVA shows a statistically significant difference in percent plasma recovery when maximum brake setting is used with a low TCF (4150 rpm for 7 minutes). No statistically significant difference was observed using maximum brake setting and high TCF (4150 rpm for 10 minutes). The significance of brake settings was consistent regardless of percent hematocrit.
Impact of Brake Settings on Plasma Recovery at Different TCF