title: Proxy markers of serum retinol concentration, used alone and in combination, to assess population vitamin A status in Kenyan children: a cross-sectional study.
abstract: BACKGROUND
  Serum retinol concentration determined by high-performance liquid chromatography (HPLC) is recommended by the World Health Organization to assess population vitamin A status. This assay is expensive, technically demanding and rarely available in developing countries. Our objective was a) to assess the diagnostic performance of proxy markers in detecting vitamin A deficiency and b) to derive decision rules based on these markers to estimate vitamin A deficiency prevalence.
  
  
  METHODS
  A survey was conducted in 15 rural primary schools in Eastern Province, Kenya, with 375 children aged 6 to 12 years (25 randomly selected per school). Serum retinol concentration <0.70 μmol/L by HPLC was used to define vitamin A deficiency. Proxy markers for vitamin A deficiency were serum concentrations of retinol binding protein (RBP), transthyretin, retinol measured by fluorometry and RBP:transthyretin molar ratio.
  
  
  RESULTS
  The prevalence of vitamin A deficiency (HPLC) was 18%. Transthyretin and RBP showed the best diagnostic performance individually, with area-under-the-curve (AUC) values of 0.96 and 0.93. When combined, and with C-reactive protein added, the AUC increased to 0.98. A simple decision rule {(-15.277 × [RBP, μmol/L] - 7.013 × [Transthyretin, μmol/L] + 0.367 × [C-reactive protein, mg/L] + 24.714) > 0.496} yielded prevalence estimates of vitamin A deficiency that is unbiased by diagnostic error.
  
  
  CONCLUSIONS
  The combination of transthyretin, RBP and C-reactive protein concentrations could eventually replace retinol concentration by HPLC in resource-poor settings as the preferred method to assess the population burden of vitamin A deficiency.
authors: Elise F
authors: EF
authors: Talsma
authors: Hans
authors: H
authors: Verhoef
authors: Inge D
authors: ID
authors: Brouwer
authors: Anne S
authors: AS
authors: Mburu-de Wagt
authors: Paul J M
authors: PJ
authors: Hulshof
authors: Alida
authors: A
authors: Melse-Boonstra
mesh_terms: D019540:Area Under Curve; D015415:Biomarkers / Q000097:blood*; D044383:Black People; D002097:C-Reactive Protein / Q000032:analysis; D002648:Child; D002851:Chromatography, High Pressure Liquid; D003430:Cross-Sectional Studies; D005260:Female; D005470:Fluorometry; D006801:Humans; D007118:Immunoassay; D007630:Kenya / Q000453:epidemiology; D008297:Male; D019095:Point-of-Care Systems; D015995:Prevalence; D012177:Retinol-Binding Proteins / Q000032:analysis*; D014801:Vitamin A / Q000097:blood*; D014802:Vitamin A Deficiency / Q000175:diagnosis* / Q000453:epidemiology*
chemical_list: D015415:Biomarkers; D012177:Retinol-Binding Proteins; D014801:Vitamin A; D002097:C-Reactive Protein