title: Long-term (in)stability of folate and vitamin B12 in human serum.
abstract: BACKGROUND
  In epidemiological research it is very important to test the stability of biomarkers as a function of both storage time and temperature. In this study the stability of both folate and vitamin B12 in human serum samples have been tested after storage at three different temperatures up to 1 year.
  
  
  METHODS
  Serum samples of 16 individuals were used in this study. The concentration of folate and vitamin B12 has been determined at T=0 and at several time points up to 1 year after storage at -20°C, -70°C and -196°C. The statistical difference from the initial value at T=0 were determined with a t-test.
  
  
  RESULTS
  Folate in serum samples remained stable at -70°C but was not stable during storage at -20°C. A fast decrease was observed after Day 4 which resulted in a stable level of about 60% of the original value measured at T=0 (p<0.001). The rank order of folate concentration in the samples, however, was not affected. The stability of vitamin B12 was good at all temperatures tested.
  
  
  CONCLUSIONS
  Measurements of folate concentrations in serum stored at -20°C are not reliable. The rank order, however, was not changed. Vitamin B12 was stable at all temperatures tested. For both folate and vitamin B12 storage at -70°C is sufficient to maintain the original concentration for 1 year. Storage at -196°C in liquid nitrogen is not necessary for these nutrients.
authors.affiliation: Laboratory for Health Protection Research, National Institute of Public Health and the Environment, Bilthoven, The Netherlands. ehjm.jansen@rivm.nl
authors.forename: Eugène H J M
authors.initials: EH
authors.lastname: Jansen
authors.forename: Piet K
authors.initials: PK
authors.lastname: Beekhof
authors.forename: Johannes W J M
authors.initials: JW
authors.lastname: Cremers
authors.forename: Erna
authors.initials: E
authors.lastname: Schenk
mesh_terms: D015415:Biomarkers / Q000097:blood; D001800:Blood Specimen Collection / Q000379:methods*; D004355:Drug Stability; D004356:Drug Storage / Q000379:methods*; D005492:Folic Acid / Q000097:blood*; D006801:Humans; D013696:Temperature; D013997:Time Factors; D014805:Vitamin B 12 / Q000097:blood*
chemical_list: D015415:Biomarkers; D005492:Folic Acid; D014805:Vitamin B 12