Biological variation of vitamins in blood of healthy individuals.

Background: Components of biological variation can be used to define objective quality specifications (imprecision, bias, and total error), to assess the usefulness of reference values [index of individuality (II)], and to evaluate significance of changes in serial results from an individual [reference change value (RCV)]. However, biological variation data on vitamins in blood are limited. The aims of the present study were to determine the intra- and interindividual biological variation of vitamins A, E, B(1), B(2), B(6), C, and K and carotenoids in plasma, whole blood, or erythrocytes from apparently healthy persons and to define quality specifications for vitamin measurements based on their biology.

Methods: Fasting plasma, whole blood, and erythrocytes were collected from 14 healthy volunteers at regular weekly intervals over 22 weeks. Vitamins were measured by HPLC. From the data generated, the intra- (CV(I)) and interindividual (CV(G)) biological CVs were estimated for each vitamin. Derived quality specifications, II, and RCV were calculated from CV(I) and CV(G).

Results: CV(I) was 4.8%-38% and CV(G) was 10%-65% for the vitamins measured. The CV(I)s for vitamins A, E, B(1), and B(2) were lower (4.8%-7.6%) than for the other vitamins in blood. For all vitamins, CV(G) was higher than CV(I), with II <1.0 (range, 0.36-0.95). The RCVs for vitamins were high (15.8%-108%). Apart from vitamins A, B(1), and erythrocyte B(2), the imprecision of our methods for measurement of vitamins in blood was within the desirable goal.

Conclusions: For most vitamin measurements in plasma, whole blood, or erythrocytes, the desirable imprecision goals based on biological variation are obtainable by current methodologies. Population reference intervals for vitamins are of limited value in demonstrating deficiency or excess.