Variance components of serum constituents in healthy individuals

Analytical, intra-individual, and inter-individual components of variance were estimated in 10 volunteers for 34 assays encompassing 22 different constituents. Replicate blood specimens were obtained four times weekly. Nine constituents were measured with more than one instrument [Technicon AutoAnalyzer II and SMAC System, Perkin-Elmer Kinetic Enzyme Analyzer KA-150, and (or) the Abbott Bichromatic Aanalyzer ABA-100]. For those constituents that were stored for randomized batch analysis, results were examined for evidence of changes during storage and within-run analytical drift. Alkaline phosphatase, cholesterol, dopamine-beta-hydroxylase, and SMAC-measured lactate dehydrogenase had a ratio of intra-individual to interindividual variance of less than 0.10, thus exhibiting a high individuality. This ratio was greater than one for sodium, carbon dioxide, and creatine kinase. Analytical variance was more than 30% of total variance for sodium, carbon dioxide, calcium, total protein, and chloride. Analytical variance was less than 20% of intra-individual variance for bilirubin, creatine kinase, KA-150-measured lactate dehydrogenase, triglycerides, and urea nitrogen. Limits for the expected difference between measurements of the same constituent for the same individual on different days are also presented.