title: Retinol-binding protein stability in dried blood spots.
abstract: BACKGROUND
  Retinol-binding protein (RBP) is accepted as a surrogate biochemical marker for retinol to determine vitamin A (VA) status. A recently developed enzyme immunoassay for RBP uses serum or whole blood stored as dried blood spots (DBS). However, the stability of RBP in DBS has not been examined.
  
  
  METHODS
  RBP stability was studied in a laboratory and in field conditions in northern Kenya. For the laboratory study, 63 DBS collected by finger prick and stored sealed in a plastic bag with desiccant were exposed to 1 of 5 time/storage-temperature treatments: (a) baseline, (b) 30 degrees C/7 days, (c) 30 degrees C/14 days, (d) 30 degrees C/28 days, and (e) 4 degrees C/38 days. Baseline RBP concentrations were compared to those obtained after the storage treatments. For the field study, 50 paired DBS and serum specimens were prepared from venous blood obtained in northern Kenya. DBS were stored in a sealed plastic bag with desiccant at ambient temperature (12 degrees C-28 degrees C) for 13-42 days, and sera were stored at -20 degrees C to -70 degrees C. Recovered RBP concentrations were compared with serum retinol for stability, correlation, sensitivity, and specificity.
  
  
  RESULTS
  RBP in DBS stored in the laboratory at 30 degrees C remained stable for 2-4 weeks, but specimens stored at 4 degrees C for 38 days produced values below baseline (P = 0.001). DBS stored under field conditions remained stable for 2-6 weeks, as demonstrated by good correlation with serum retinol, a result that suggests that RBP in DBS will have good sensitivity and specificity for predicting VA deficiency.
  
  
  CONCLUSIONS
  RBP in DBS can withstand storage at a relatively high ambient temperature and thus facilitate accurate VA assessments in populations in locations where serum collection and storage are unfeasible.
authors.affiliation: Department of Anthropology, University of Washington, Seattle, WA 98195-3100, USA. masakof@u.washington.edu
authors.forename: Masako
authors.initials: M
authors.lastname: Fujita
authors.forename: Eleanor
authors.initials: E
authors.lastname: Brindle
authors.forename: Jane
authors.initials: J
authors.lastname: Shofer
authors.forename: Philip
authors.initials: P
authors.lastname: Ndemwa
authors.forename: Yeri
authors.initials: Y
authors.lastname: Kombe
authors.forename: Bettina
authors.initials: B
authors.lastname: Shell-Duncan
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: O'Connor
mesh_terms: D001800:Blood Specimen Collection; D005260:Female; D006801:Humans; D007630:Kenya; D009656:North America; D012177:Retinol-Binding Proteins / Q000032:analysis*; D012680:Sensitivity and Specificity; D013696:Temperature; D013997:Time Factors; D014801:Vitamin A / Q000097:blood; D014802:Vitamin A Deficiency / Q000175:diagnosis
chemical_list: D012177:Retinol-Binding Proteins; D014801:Vitamin A