Abstract
The purpose of reference values for vitamin concentrations in serum, plasma and whole blood and the need for standardization of vitamin assay methods were described. The nutritional assessment of vitamin data is a comparative decision-making process in which a laboratory test result for an individual is compared with a reference value. Therefore, reliable reference values are required for all vitamin assays in clinical laboratory. The reference values should be provided by the candidate reference method or routine measurement procedure both of which have a demonstrated record of traceability of accuracy from the reference measurement procedure. The term "traceability chain" is used to refer to an unbroken chain of comparisons relating the routine measurement procedure to a certified concentration (expressed as SI unit) of the primary standard determined by the reference measurement procedure. The traceability chain was combined by the reference standard (e.g., NIST SRM) between the reference measurement procedure and the routine measurement procedure. The above process is referred to as "standardization". Nowadays, the reference measurement procedures are selected for measurements of folate and vitamin D in clinical specimens, and the candidate reference methods for vitamin A, vitamin D, vitamin E, vitamin B_1, vitamin B_<12>, folate and vitamin C. The reference values provided by the candidate reference method was available in vitamin A, vitamin D, vitamin E, vitamin B_1, vitamin B_<12>, folate and vitamin C. Decision limits, the analytical concentration that reflected the nutritional status of individuals as "deficiency", "marginal deficiency" or "adequate", for vitamin D, vitamin B_1, folate and vitamin C were also described.
