title: Difference between free circulating plasma and serum DNA in patients with colorectal liver metastases.
abstract: BACKGROUND
  Previous studies suggest that the amount of circulating cell-free DNA in plasma or serum may be a promising marker for diagnosis and prediction of prognosis in patients with tumours. However, it is unclear whether DNA from plasma or from serum better reflects the clinical status.
  
  
  METHODS
  To investigate the possible difference between serum DNA and plasma DNA levels, blood was collected from 26 patients with liver metastases and 28 age-matched healthy donors. The patients had clinical follow-up after surgery (median 23 months). DNA was quantified by two independent methods: real-time quantitative PCR (TaqMan) and fluorimetric DNA quantitation (Picogreen reagent).
  
  
  RESULTS
  Serum DNA and plasma DNA levels did not correlate and each had a different relationship with diagnosis and prognosis. Only serum DNA was significantly associated with the presence of liver metastases, whereas only plasma DNA was predictive for recurrences. Typically, serum DNA amounts were higher than plasma in 24 out of 26 patients.
  
  
  CONCLUSIONS
  This difference between plasma and serum reflects an in vitro process that occurs during clotting. High DNA increase in serum represents an indirect, yet tumour-related process. Plasma DNA levels better represent in vivo levels of circulating DNA. This has implications forfuture studies.
authors.affiliation: Department of Clinical Chemistry, University Medical Centre Nijmegen, The Netherlands. j.dekok@ckcl.azn.nl
authors.forename: Myriam A M A
authors.initials: MA
authors.lastname: Thijssen
authors.forename: Dorine W
authors.initials: DW
authors.lastname: Swinkels
authors.forename: Theo J M
authors.initials: TJ
authors.lastname: Ruers
authors.forename: Jacques B
authors.initials: JB
authors.lastname: de Kok
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor / Q000097:blood* / Q000235:genetics; D015179:Colorectal Neoplasms / Q000097:blood* / Q000235:genetics / Q000473:pathology / Q000601:surgery; D004273:DNA, Neoplasm / Q000097:blood*; D006801:Humans; D008113:Liver Neoplasms / Q000097:blood* / Q000235:genetics / Q000556:secondary*; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000097:blood / Q000235:genetics; D011379:Prognosis; D015203:Reproducibility of Results
chemical_list: D014408:Biomarkers, Tumor; D004273:DNA, Neoplasm