Evolution of reference materials for the determination of organic nutrients in food and dietary supplements-a critical review.

For over 40 years, food-matrix certified reference materials (CRMs) have been available for determination of trace element content, and a wide variety of materials are available from most producers of CRMs. However, the availability of food-matrix CRMs for organic nutrients has been more limited. The European Commission (EC) Bureau Communautaire de Référence (BCR) and the National Institute of Standards and Technology (NIST) introduced food-matrix CRMs with values assigned for vitamins and other organic nutrients such as fatty acids and carotenoids in the 1990s. The number of organic nutrients for which values were assigned has increased significantly in the past decade, and the approach and analytical methods used for assignment of the certified values have also evolved. Recently, dietary supplement-matrix CRMs such as multivitamin tablets with values assigned for vitamins and carotenoids, and fish and plant oils with values assigned for fatty acids have appeared. The development, evolution, and improvement of food- and dietary supplement-matrix CRMs for determination of vitamins, carotenoids, and fatty acids are described, with emphasis on CRMs made available in the past 10 years. Recent food and dietary supplement CRMs for the determination of organic nutrients include infant formula, multivitamin tablets, milk and egg powders, breakfast cereal, meat homogenate, blueberries, soy flour, fish and plant oils, dry cat food, and protein drink powder. Many of these food- and supplement-matrix CRMs have values assigned for over 80 organic and inorganic nutrients, toxic elements, proximates, and contaminants. The review provides a critical assessment of the challenges and evolving improvements in the production and the analytical methods used for value assignment of these CRMs. The current status and future needs for additional food- and dietary supplement-matrix CRMs for organic nutrients are also discussed. Graphical abstract Food Composition Triangle with currently-available food-matrix certified reference materials (CRMs) for the determination of organic nutrients positioned according to fat, protein, and carbohydrate composition.

Cholesterol screening: comparative evaluation of on-site and laboratory-based measurements.

We measured cholesterol in capillary blood samples from 9683 volunteers over a four-day on-site community screening program, using the "Reflotron" desk-top analyzer (Boehringer-Mannheim Diagnostics, Indianapolis, IN). We also measured cholesterol in venous blood samples from 3% of those screened (a) with the Reflotron at the screening sites, (b) in a qualified hospital clinical laboratory, and (c) in a Centers for Disease Control standardized lipoprotein research laboratory. The sensitivity (and specificity) of the Reflotron measurements, with use of the lipoprotein laboratory measurements as the point of reference, was 0.95 (0.73) in capillary blood samples and 0.88 (0.93) in venous blood samples, compared with 0.99 (0.87) in the hospital clinical laboratory. The Reflotron measurements correlated less well with the lipoprotein laboratory values in both venous blood (r = 0.91) and capillary blood (r = 0.89) samples than did the clinical laboratory values (r greater than 0.99). Furthermore, the capillary blood measurements averaged 7% higher than venous measurements when both kinds of samples were analyzed in the Reflotron.

Regional interlaboratory standardization of determinations of cholesterol, high-density lipoprotein cholesterol, and triglycerides.

The Clinical Chemistry Forum of Central Virginia initiated a lipid standardization program to help ensure that its members meet the current National Cholesterol Education Program guidelines for cholesterol testing, and to standardize assays of high-density lipoprotein (HDL) cholesterol and triglycerides so as to provide accurate lipid profiles. We found that freshly collected, never-frozen human sera must be used to assess interlaboratory accuracy for cholesterol, HDL cholesterol, and triglycerides assays, and that at least 23 samples are required to detect a 3% bias with 90% power when the between-laboratory imprecision (CV) is 3%. After recalibration, all 12 laboratories had a mean HDL cholesterol bias less than or equal to 5%, nine of 10 laboratories had a mean HDL cholesterol bias less than or equal to 40 mg/L for samples with values less than or equal to 570 mg/L, and 10 of 12 laboratories had a mean triglycerides bias less than or equal to 10% for fresh human sera split between participants and the Centers for Disease Control. Pools of frozen human sera were shown to have matrix biases greater than 3% for cholesterol in seven of 11 laboratories, and greater than 40 mg/L for HDL cholesterol in six of nine laboratories.