Biochemical assessment of vitamins and trace metals.

The choice of nutritional assessment tests must be made with care, as the available tests may reflect recent dietary intakes or body tissue stores to different degrees. The interpretation of nutritional assessment tests is complicated by the dynamic nature and broad range of nutrient intake and metabolism and by a relative lack of age- and sex-specific reference ranges. The latter problem can be minimized by the use of function-based methods, such as the measurement of vitamin-dependent red cell enzyme activities to assess B vitamin status; however, few suitable function-based methods are now available, and more research in this area is needed. Because calibration standards and quality control materials may not be readily available, laboratory analysts planning nutritional assessment testing must be especially careful in establishing the credibility of assays and the quality control program. Recent advances in analytic methodology include the specificity offered by HPLC techniques and methodologies that provide simultaneous determination of more than one nutrient (or form of nutrient) in a single procedure. Examples of the latter include HPLC methods that provide B vitamin or fat-soluble vitamin profiles, and emission spectrometry techniques that provide trace metal profiles. Further work in providing useful nutritional assessment profiles and convenient automated methods is needed.