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Assessment of Factor V Activity in Apheresis Platelet Units: Implications for Management of FV Deficiency


 
 
 Factor V (FV) deficiency is a rare but significant disorder associated with potentially life-threatening bleeding. Management may involve plasma infusion to increase FV activity. Although the majority (~80%) of FV is present in the plasma, approximately 20% is stored in platelet (PLT) alpha granules. As such, allogeneic PLT infusion is another strategy that has been proposed in the literature to raise FV levels. Although the rationale for this approach is understandable, these recommendations are based largely on anecdotal reports. Since FV is the most labile coagulation factor from an in vitro standpoint and given that allogeneic PLTs are stored at room temperature for 5–7 days after collection, we hypothesized that there would be low FV activity in PLT units and tested our hypothesis by assessing FV levels across PLT products.
 
 
 
 PLTs were aliquoted from apheresis units only, including those with PLT additive solution (PAS) and from non-PAS units (N=26) on post-collection days 3–6. Supernatant was prepared from PLTS by centrifugation (5000 rpm X 5 min) and was stored at -80oC until analyzed. PLT lysate (PL) was prepared by freezing (-80oC) then thawing (370 C) followed by centrifugation (10,000 rpm X 10 min). FV activity was tested in the PLT unit supernatant and lysate using a clinical-grade assay based on prothrombin time correction of FV deficient plasma and expressed as percent activity; reference range for normal plasma FV levels at our facility is 50–150% activity. Statistical analysis was performed using student t test. The data were expressed as mean ± SD (P-value <0.05 considered significant).
 
 
 
 FV activity was markedly low in PAS PLT units, in both supernatant (3.70% ± 1.02%) as well as PL (3.26% ± 1.02%); N=16. FV activity in non-PAS PLT units (N= 10) was also somewhat low relative to reference range plasma levels in both supernatant (44.55% ± 6.46%) and PL (39.67% ± 6.33%); however, it was significantly higher (P < .001) when compared to PAS PLT units. FV activity from aliquots extracted from the same PAS PLT units and examined serially over storage time (N=3) showed FV levels on day 3 of storage (supernatant 5.03% ± 1.41%; PL: 3.89% ± 1.03%) to be not significantly different than levels measured on day 5 of storage (supernatant: 3.10% ± 0.57%; PL: 2.61% ± 0.41%; P=0.4).
 
 
 
 FV is substantially depleted across PLT components, with particularly low levels observed in PAS PLTs. Given comparable supernatant and PL FV levels, there appears to be little FV reserve available in PLT lysate. Based on these data, plasma should be considered a first-line therapy for most non-complex FV deficiency-associated bleeds. If PLTs are considered for additional use, then non-PAS PLT units should be preferentially employed.
