title: Influence of cell-free DNA in plasma on real-time polymerase chain reaction for determination of residual leucocytes in platelet concentrates.
abstract: OBJECTIVE
  Real-time quantitative (RQ) polymerase chain reaction (PCR) can be used to determine the number of residual leucocytes in leucocyte-reduced platelet concentrates (LR-PCs), which should contain < 3.3 leucocytes/ micro l. In this study we investigated the extent to which cell-free DNA, known to be present in plasma, might interfere with this determination. In this study, RQ-PCR was employed to determine the following: the influence of filtration of platelet concentrates (PCs) on the amount of cell-free DNA; the variation in concentration of cell-free DNA between the buffy coats (BCs) of different donors; and the amount of cell-free DNA during storage and processing of whole blood.
  
  
  METHODS
  PCs were sampled before and after filtration (n = 5), BCs were sampled (n = 100) and whole blood units were sampled < 2 h and 16-20 h after collection, and the BCs were also sampled after processing the whole blood (n = 10). Samples were centrifuged to obtain cell-free plasma in which the amount of cell-free DNA was determined using an RQ-PCR for the albumin gene.
  
  
  RESULTS
  The amount of cell-free DNA was not influenced by filtration of the PCs [1.7 +/- 0.8 vs. 1.5 +/- 0.8 leucocyte-equivalents (eq)/ micro l]. However, the amount of cell-free DNA in plasma of the BCs varied considerably, from 0.1 to 18.2 leucocyte-eq/ micro l (median = 1.5 leucocyte-eq/ micro l; mean +/- SD: 2.2 +/- 2.4 leucocyte-eq/ micro l). In 18% of the BCs the amount cell-free DNA was > 3.3 leucocyte-eq/ micro l. The amount of cell-free DNA increased during storage, from 0.3 +/- 0.3 leucocyte-eq/ micro l (< 2 h after collection) to 0.9 +/- 0.6 leucocyte-eq/ micro l (16-20 h after collection) and, after processing the whole blood, to 2.0 +/- 2.0 leucocyte-eq/ micro l.
  
  
  CONCLUSIONS
  Variable amounts of cell-free DNA in plasma will interfere if RQ-PCR is applied to estimate leucocyte numbers in leucocyte-reduced PCs.
authors.affiliation: Sanquin Blood Bank north-west Region, Amsterdam, the Netherlands. m.dijkstra@sanquin.nl
authors.forename: M J
authors.initials: MJ
authors.lastname: Dijkstra-Tiekstra
authors.forename: R N I
authors.initials: RN
authors.lastname: Pietersz
authors.forename: H W
authors.initials: HW
authors.lastname: Reesink
authors.forename: C E
authors.initials: CE
authors.lastname: van der Schoot
mesh_terms: D016477:Artifacts; D001792:Blood Platelets; D002469:Cell Separation; D003199:Computer Systems; D004247:DNA / Q000097:blood*; D005374:Filtration; D006801:Humans; D007958:Leukocyte Count; D010949:Plasma / Q000166:cytology*; D016133:Polymerase Chain Reaction / Q000379:methods*
chemical_list: D004247:DNA