We hypothesized that chemerin levels are increased in patients with RA with clinical disability in comparison with patients with RA without clinical disability, and this increase is independent of other adipokines, cytokines or E-selectin. To test this hypothesis, we planned a correlation analysis between two continuous variables; the first was adipokines as independent variables and DAS28-CRP or HAQ-DI scores as the dependent variables. Using the results described in a previous study performed by Ha et al.10, these authors observed that chemerin levels correlated with the DAS-28 score in patients with RA (r = 0.31, p < 0.01).

Thus, we proceeded to assume the following:

A result of the Spearman correlation tests of 0.31, with a significant p-value, could be sufficient to reject the null hypothesis of no correlations between the markers assessed in this study and the HAQ-DI score (functional disability).

We chose a statistical power of 0.8 and a type I error probability of 0.05.

Thus, we found that 80 patients with RA were estimated to be required to reject the null hypothesis of no correlations between these markers and the HAQ-DI score.

Quantitative variables are described by medians and ranges, and qualitative variables are described by frequencies (%). According to the Shapiro–Wilk test, the adipokines, cytokines and E-selectin levels showed a nonparametric distribution. Therefore, we assessed the differences in the medians of adipokines, cytokines and E-selectin levels between patients with RA with functional disability and patients with RA without functional disability using the Mann–Whitney U test. The chi-square test was used to demonstrate differences between proportions. Spearman’s tests were utilized to determine the correlations of the HAQ-Di and DAS28-ESR with chemerin, other adipokines, pro-inflammatory cytokines and E-selectin.

The Kruskal–Wallis test was utilized for comparisons of the sum of ranks between three groups: (a) patients with functional disability and disease activity (HAQ-Di, score ≥ 0.6 + High DAS28-ESR, score > 3.2); (b) patients with functional disability without disease activity (HAQ-Di, score < 0.6 + Low DAS28-ESR, score ≤ 3.2); and (c) patients without functional disability (non-disabled).

The cut-off for statistical significance was p ≤ 0.05. Statistical analyses were performed using R version 4.0.0.

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