title: Long-term stability of cancer biomarkers in human serum: biomarkers of oxidative stress and redox status, homocysteine, CRP and the enzymes ALT and GGT.
abstract: OBJECTIVE
  Five frequently used biomarkers in cancer research and epidemiological studies were tested for their assay stability upon storage of serum for 12 months at -20 and -70/-80°C.
  
  
  METHODS
  The biomarker assays include reactive oxygen metabolites (ROM), the total thiol levels (TTL), homocysteine (HCy), C-reactive protein (HS-CRP) and two liver enzymes, alanine aminotransferase (ALT) and γ-glutamyltransferase (GGT).
  
  
  RESULTS
  The assays for ROM, HCy, HS-CRP and GGT were stable in human serum samples at the two temperatures tested. The two other assays TTL and ALT, however, showed statistically significant differences in their stability between -20 and -80°C.
  
  
  CONCLUSIONS
  Therefore, storage at -80°C is advised to maintain a reliable assay outcome when serum samples have to be stored for longer periods.
authors.forename: Eugène
authors.initials: E
authors.lastname: Jansen
authors.forename: Piet
authors.initials: P
authors.lastname: Beekhof
authors.affiliation: 2Department of Biochemistry, Medical Academy, Lithuanian University of Health Sciences, A Mickeviciaus 9, LT-44307, Kaunas, Lithuania.
authors.forename: Dale
authors.initials: D
authors.lastname: Viezeliene
authors.forename: Vladimira
authors.initials: V
authors.lastname: Muzakova
authors.forename: Jiri
authors.initials: J
authors.lastname: Skalicky
mesh_terms: D000410:Alanine Transaminase / Q000097:blood*; D014408:Biomarkers, Tumor / Q000097:blood*; D002097:C-Reactive Protein / Q000378:metabolism*; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D009369:Neoplasms / Q000097:blood*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology*; D005723:gamma-Glutamyltransferase / Q000097:blood*
chemical_list: D014408:Biomarkers, Tumor; D006710:Homocysteine; D002097:C-Reactive Protein; D005723:gamma-Glutamyltransferase; D000410:Alanine Transaminase
keywords: C-reactive protein; alanine aminotransferase; cancer biomarkers; homocysteine; hydroperoxides; stability; storage; total thiols; γ-glutamyltransferase