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

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.

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).

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.

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.