Quality assurance programs for vitamin A and E in serum: are we doing enough to assess laboratory performance?

OBJECTIVES: Monitoring serum vitamin A (retinol) and vitamin E (α-tocopherol) concentrations is common practice for assessing nutritional status. Measurement of these vitamins can be challenging due to several factors. Whilst the RCPAQAP Vitamins: Serum Program assists participating laboratories in harmonisation, the materials provided do not contain the analogues of retinol and α-tocopherol that may be present in real patient samples. We aimed to assess participants' capacity to accurately report retinol and α-tocopherol in the presence of the vitamin E analogues tocopherol acetate and γ-tocopherol. METHODS: A supplementary series of a control sample and three matched spiked samples were distributed to each laboratory participating in the Program. Retinol and α-tocopherol results for each spiked sample were compared to the results of the control sample submitted by each participant. Acceptability of retinol and α-tocopherol results was determined based on the RCPAQAP allowable performance specifications (APS). RESULTS: Thirteen participants returned results for the supplementary sample series. Interference from α-tocopherol acetate was observed with results below the APS in 30 % (n=4) of laboratories for retinol quantification and in 23 % (n=3) for α-tocopherol quantification. One laboratory returned results above the APS for α-tocopherol when γ-tocopherol was present. CONCLUSIONS: This supplementary sample series has shown that the presence of vitamin E analogues can lead to the over or under estimation of nutritional status by some participants. Affected laboratories are encouraged to review their analytical procedures. To further assess laboratory competence, EQA providers should consider using patient samples or spiked challenge samples.

Laboratory medicine best practice guideline: vitamins a, e and the carotenoids in blood.

Despite apparent method similarities between laboratories there appear to be confounding factors inhibiting uniform reporting and standardisation of vitamin assays. The Australasian Association of Clinical Biochemists (AACB) Vitamins Working Party, in conjunction with The Royal College of Pathologists of Australasia Quality Assurance Programs, has formulated a guideline to improve performance, reproducibility and accuracy of fat-soluble vitamin results. The aim of the guideline is to identify critical pre-analytical, analytical and post-analytical components of the analysis of vitamins A, E and carotenoids in blood to promote best practice and harmonisation. This best practice guideline has been developed with reference to the Centers for Disease Control and Prevention (CDC) "Laboratory Medicine Best Practices: Developing an Evidence-Based Review and Evaluation Process". The CDC document cites an evaluation framework for generating best practice recommendations that are specific to laboratory medicine. These 50 recommendations proposed herein, were generated from a comprehensive literature search and the extensive combined experience of the AACB Vitamins Working Party members. They were formulated based on comparison between an impact assessment rating and strength of evidence and were classified as either: (1) strongly recommend, (2) recommend, (3) no recommendation for or against, or (4) recommend against. These best practice recommendations represent the consensus views, in association with peer reviewed evidence of the AACB Vitamins Working Party, towards best practice for the collection, analysis and interpretation of vitamins A, E and carotenoids in blood.