title: Vitamin B1 and B6 method harmonization: comparison of performance between laboratories enrolled in the RCPA Quality Assurance Program.
abstract: OBJECTIVE
  The RCPA Quality Assurance Program (RCPA QAP) offers monthly proficiency testing for vitamins A, B1, B6, β-carotene, C and E to laboratories worldwide. A review of the results submitted for the whole blood vitamin B1/B6 sub-program revealed a wide dispersion. Here we describe the results of a methodology survey for vitamins B1 and B6.
  
  
  METHODS
  A questionnaire was sent to thirteen laboratories. Eleven laboratories were returning QAP results for vitamin B1 (thiamine diphosphate) and five were returning results for vitamin B6 (pyridoxal-5-phosphate).
  
  
  RESULTS
  All nine respondents provided a clinical service for vitamins B1 and B6. HPLC with fluorescence detection was the most common method principle. For vitamin B1, six respondents used a commercial assay whilst three used in-house methods; whole blood was the matrix for all. For vitamin B6, five respondents used commercial assays and four used in-house assays. The choice of matrix for vitamin B6 varied with three respondents using whole blood and five using plasma for analysis. Sample preparation incorporated protein precipitation and derivatization steps. An internal standard was employed in sample preparation by only one survey respondent.
  
  
  CONCLUSIONS
  The immediate result of this survey was the incorporation of plasma vitamin B6 into the RCPA QAP vitamin program. The absence of an internal standard in current vitamin B1 and B6 assays is a likely contributor to the wide dispersion of results seen in this program. We recommend kit manufacturers and laboratories investigate the inclusion of internal standards to correct the variability that may occur during processing.
authors: Australasian Association of Clinical Biochemists, Vitamins Working Party, Australia.
authors: Kirsten E
authors: KE
authors: Hoad
authors: Lambro A
authors: LA
authors: Johnson
authors: Gerald A
authors: GA
authors: Woollard
authors: Trevor A
authors: TA
authors: Walmsley
authors: Scott
authors: S
authors: Briscoe
authors: Lisa M
authors: LM
authors: Jolly
authors: Janice P
authors: JP
authors: Gill
authors: Ronda F
authors: RF
authors: Greaves
mesh_terms: D001774:Blood Chemical Analysis / Q000592:standards*; D002851:Chromatography, High Pressure Liquid / Q000592:standards; D006801:Humans; D059021:Laboratory Proficiency Testing; D012016:Reference Values; D011795:Surveys and Questionnaires; D013831:Thiamine / Q000097:blood*; D025101:Vitamin B 6 / Q000097:blood*
chemical_list: D025101:Vitamin B 6; D013831:Thiamine