Circulating levels of eNAMPT were significantly higher in T2DM patients than in control individuals (P < 0.001). Correlations of eNAMPT with FBG (r = 0.621, P < 0.01), insulin (r = 0.416, P < 0.01), HOMA-IR (r = 0.518, P < 0.01), HbA1c (r = 0.388, P < 0.01), IL-34 (r = 0.312, P < 0.01), IRAPe (r = −0.380, P < 0.01), and irisin (r = −0.494, P < 0.01) were observed. This evidence concerns the gene FNDC5 and type 2 diabetes mellitus.