Carotenoids, retinol and tocopherols in blood: Comparability between serum and plasma (Li-heparin) values

Objective: To assess the comparability of concentrations of retinol, α- and γ-tocopherols and individual carotenoids in serum and (Li-hep) plasma over a wide range of concentrations. Material and methods: One hundred sixty-six pairs of samples (serum and lithium-heparin plasma) were analyzed by a quality-controlled HPLC method. Means and 95% confidence intervals, differences, interchangeability and the degree of agreement (Bland–Altman plot) were calculated. Results: Distribution of all analytes in the two matrices are comparable and interchangeable with minor quantitative adjustments. Within the range of concentrations assessed, the degree of agreement was high, although some differences were observed for minor components with greater analytical imprecision. Conclusions: The results indicate an acceptable degree of agreement using either of the two matrices for the analytes assessed except possibly for minor blood components. For retinol and α-tocopherol, the comparability and interchangeability of results below the cut-off points for inadequacy need further confirmation.