Biological and Analytic Components of Variation in Long-Term Studies of Serum Constituents in Normal Subjects

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Abstract
A study of blood constituents in normal individuals was undertaken to (a) estimate the contribution of biological and analytical factors to the variation of constituents over an extended time period; (b) to explore whether such tests can be used to derive meaningful personal blood "profiles"; and (c) to determine when analytic variation may become large enough to assume medical significance. This first paper describes procedures for subject selection, the laboratory methods employed, and evaluates analytic standard deviations. A group of 68 normal subjects was selected after medical evaluation. Sera were collected and analyzed in duplicate weekly for 10 to 12 weeks. Analytic deviation was estimated from the results of concurrent daily analyses of sterile pools of human serum. Laboratory procedures were introduced to reduce analytic deviation and to allow more accurate estimation of biological components of variation within and among individuals.