Biological Variation of Interleukin-1I2, Interleukin-8 and Tumor Necrosis Factor-I- in Serum of Healthy Individuals

Components of biological variation can be used to assessthe usefulness of reference values, to evaluate thesignificance of changes in serial results from an individualand to define objective analytical goals. The aimof the study was to assess, in 15 healthy subjects studiedat regular monthly intervals over a period of 6consecutive months, the biological variation of interleukin-1I2 (IL-1I2), interleukin-8 (IL-8), and tumor necrosisfactor-I- (TNF-I-). Biological variation data (within-subjectand between-subject coefficient of variation(CV)) were determined using a simple nested analysisof variance. Derived parameters (index of individuality,reliability coefficient and critical diferences) were calculatedfrom within-subject and between-subject CV.The mean and standard deviation (SD), within-subjectCV, between-subject CV, index of individuality and reliabilitycoefficient were as follows: for IL-1I2, 0.67(0.32) pg/ml, 30%, 36%, 0.85, and 0.76; for IL-8, 3.68(1.45) pg/ml, 24%, 31%, 0.85 and 0.75; and for TNF-I-,3.14 (1.87) pg/ml, 43%, 29%, 1.56 and 0.50, respectively.We conclude that between-subject variationand within-subject variation are quite similar for IL-1I2and IL-8 and are relatively high for the three cytokinesstudied. Index of individuality is less than 1.4 for IL-1I2and IL-8, and thus reference intervals based on populationstudies are of limited value. On the contrary, theindex of individuality for TNF-I- is greater than 1.4 andreference values can be used for diagnosis. Qualitygoals for imprecision are easily achieved for the threecytokines with current methodology.