FNDC5 and Sepsis: After adjustment for the APACHE II score and significant laboratory biomarkers, lower circulating irisin both at enrollment and one week after sepsis onset were independently associated with 28-day mortality (HR 0.44, 95% C.I. 0.26–0.77, p = 0.004 and HR 0.37, 95% C.I. 0.23–0.58, p < 0.001, respectively) (Table 5).