title: The Glass Slide Extraction System Snap Card Improves Non-Invasive Prenatal Genotyping in Pregnancies with Antibodies.
abstract: BACKGROUND
  Determination of fetal blood groups in maternal plasma samples critically depends on adequate pre-analytical steps for optimal amplification of fetal DNA. We compared the extraction of cell-free DNA by binding on a glass surface (BCSI SNAP™ Card) with an automated system based on bead technology (MagnaPure compact™).
  
  
  METHODS
  Maternal blood samples from 281 pregnancies (7th-39th week of gestation) with known antibodies were evaluated in this study. Both the SNAP card and the MagnaPure method were applied to isolate DNA in order to directly compare the amplification in a single base extension assay and/or real-time PCR.
  
  
  RESULTS
  The mean concentration of total DNA obtained by the SNAP card (33.8 ng/µl) exceeded more than twofold that of MagnaPure extraction (15.7 ng/µl). SNAP card-extracted samples allowed to detect 3.7 single nucleotide polymorphisms (SNPs) versus 2.5 SNPs in MagnaPure extracts to control for traces of fetal DNA. This difference is highest for samples from 7th-13th week of gestation.
  
  
  CONCLUSIONS
  The SNAP card system improves DNA extraction efficacy for prenatal diagnosis in maternal blood samples and provides an at least eightfold higher total amount of DNA for the ensuing analysis. Its advantage is most evident for samples from early stages of pregnancy and thus especially valuable for pregnancies with antibodies.
authors.affiliation: Medical Hospital 'Links der Weser', Gesundheit Nord, Department Internal Medicine, Bremen, Germany.
authors.forename: Thomasz
authors.initials: T
authors.lastname: Adamczyk
authors.affiliation: German Red Cross Blood Transfusion Service NSTOB, Institute Oldenburg, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Doescher
authors.affiliation: Blood Cell Storage, Inc., Seattle, WA, USA.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Haydock
authors.affiliation: Blood Cell Storage, Inc., Seattle, WA, USA.
authors.forename: Russ
authors.initials: R
authors.lastname: Aldrich
authors.affiliation: German Red Cross Blood Transfusion Service NSTOB, Institute Oldenburg, Germany.
authors.forename: Eduard K
authors.initials: EK
authors.lastname: Petershofen
authors.affiliation: German Red Cross Blood Transfusion Service NSTOB, Institute Springe, Germany.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Müller
keywords: Cell-free DNA; DNA extraction; Non-invasive prenatal genotyping