title: A dried serum spot assay for vitamin B(12).
abstract: BACKGROUND
  A newly developed dried serum spot (DSS) vitamin B(12) assay compares well with a conventional reference serum vitamin B(12) microbiological assay (r=0.97, n=161) and demonstrates adequate within (CV% <6) and between assay (CV% <10) reproducibility.
  
  
  METHODS
  The consistency of long-term vitamin B(12) assay performance was supported and validated using a reconstituted International Reference Serum (IRR 81/563) stored at -70 degrees C as both whole serum aliquots and as DSS. The inclusion of such reference sera also allows accurate comparisons to be made with data from other laboratories and studies.
  
  
  RESULTS
  The DSS matrix displays excellent characteristics of pre-analytical serum vitamin B(12) stability at ambient temperatures with less than 5% loss of activity occurring at 4 degrees C, 20 degrees C and 37 degrees C after 7 days of storage in the dark.
  
  
  CONCLUSIONS
  These qualities underline the suitability of the DSS matrix for epidemiological screens of serum vitamin B(12) levels by obviating the need for costly refrigeration and specialised handling of serum samples and allowing economic transportation using the basic postal service.
authors.affiliation: Department of Haematology, St James's Hospital, Dublin 8, Ireland. sdobroin@stjames.ie
authors.forename: Sean D
authors.initials: SD
authors.lastname: O'Broin
authors.forename: Brian P
authors.initials: BP
authors.lastname: Kelleher
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry; D001774:Blood Chemical Analysis / Q000379:methods*; D003890:Desiccation; D005492:Folic Acid / Q000097:blood; D015203:Reproducibility of Results; D044967:Serum / Q000737:chemistry*; D013696:Temperature; D014805:Vitamin B 12 / Q000097:blood* / Q000378:metabolism
chemical_list: D005492:Folic Acid; D014805:Vitamin B 12; D001205:Ascorbic Acid