Objectives: The aim of this study was to examine the reference change value defined as a normal difference in serial test results to investigate clinically significant changes in a given proportion of all healthy persons. Methods: In all, 18 volunteers were included in a cross-sectional and methodological study. The participants provided 5-mL blood samples twice a day, before and after having breakfast, 3 times in 15-day periods. The levels of glycose and insulin were evaluated biochemically and with a hormone auto-analyzer. Biological variation, the reference change value, and the individual index were calculated. Results: The mean participant age±SD was 40.1±7.81 years, and the median age was 41.0 years (min: 27, max: 55 years). Twelve (66.67%) were female and 6 (33.33%) were male. While fasting blood sugar (FBS) was influenced by both time and individual characteristics (p=0.030 and 0.006, respectively), fasting insulin resistance (FIR) changed over time, but was not influenced by individual characteristics, according to the LOG10 base (p=0.796 and p=0.015, respectively). The level 1 FBS intra-individual variation was 7.62 and the inter-individual variation was 7.69. For level 2, the intra-individual variation was 7.71 and the inter-individual variation was 7.65. The intra-individual variation < the inter-individual variation for FIR in both level 1 (15.50<18.44) and level 2 (15.69<18.37). Conclusion: Measurements of glucose and insulin levels should be examined using the analytic variation values of the device. This study demonstrates the importance of analytical variation, intra- and inter-individual variation, the index of individuality, and reference change value.
Corresponding Author: Fatma Nesrin Turan