Model diagnostics of the curve fitting of IL-1β (a) and IP-10 (b)."Residuals vs. Fitted" and "Scale-Location" show that a trend appears in the residuals distribution for concentrations below 400 ng/mL. The “Q-Q plot” suggests that residuals are not normally distributed. Whilst this does not affect the goodness of the coefficient estimation, it impairs the t-distribution and thus renders the use of p-values meaningless. The Cook’s distance suggests that 2 of the most diluted samples could be considered outliers in their influence on the model fitting. However, Cook’s distance has no unambiguous interpretation and the best decision is to look at the original distribution, where the 2 incriminated points show no indication of anomalous position. The red dashed lines delimited the 95% of CI.