Analytical and clinical comparison between two different analytical methods for the measurement of circulating insulin in patients with metabolic-dysfunction associated steatotic liver disease

BACKGROUND: Reliable circulating insulin determination in patients with metabolic-dysfunction associated steatotic liver disease (MASLD) is important to assess the entity of insulin resistance, the most important pathogenetic mechanism involved in the onset and progression of the disease. However, one of the most important issues concerning insulin measurement is the lack of standardization across laboratories worldwide. The aim of this study was to compare two different analytical methods for the measurement of circulating insulin in subjects with MASLD and to explore their reliability through the analysis of clinical data.METHODS: Overall, 160 subjects with MASLD at ultrasound (median age: 51 [95% CI: 49-54]; M/F: 114/46) with available plasma and serum samples were included in the study. Circulating insulin was measured by the fully automated Alinity I system (Abbott Laboratories, Abbott Park, IL, USA) and by Bio-Plex Luminex (Bio-Rad Laboratories) 200 System (Bio-Rad Laboratories, Hercules, CA, USA).RESULTS: Median insulin levels measured by Bio-Plex (Bio-Rad Laboratories) and Alinity I (Abbott Laboratories) were not comparable in our study cohort (527 vs. 400 pg/mL, respectively; P<0.001). Passing and Bablok regression analysis showed a correlation coefficient of 0.45 (95% CI: 0.322-0.569), but we observed both systematic and proportional differences between the two methods; furthermore, Bland-Altman plot analysis indicated that the two methods cannot be used interchangeably. Alinity I (Abbott Laboratories) insulin significantly correlated with BMI, AST, ALT, glucose, triglycerides and HDL-cholesterol levels, while Bio-Plex (Bio-Rad Laboratories) insulin correlated with AST, ALT and HDL-cholesterol levels. At multivariable regression analysis, both Alinity I (Abbott Laboratories) and Bio-Plex (Bio-Rad Laboratories) insulin were significantly associated with liver stiffness (rpartial=0.32, P<0.001 and rpartial=0.17, P=0.032, respectively), but only Alinity I (Abbott Laboratories) insulin was significantly associated with CAP (rpartial=0.50, P<0.001).CONCLUSIONS: Bio-Plex insulin (Bio-Rad Laboratories) should be used with caution and only for research purposes, while Alinity system (Abbott Laboratories) is confirmed as the most reliable platform in the clinical setting. However, it is important to continue through the process of insulin harmonization to ensure reliable, comparable and reproducible results.