When stratified, the PreDM model (χ2(6) = 15.87, p = 0.014; AUC = 0.794, 95% CI 0.674–0.883) showed a nonsignificant protective trend for irisin (OR = 0.72, p = 0.362), whereas in T2DM (χ2(6) = 19.56, p = 0.003; AUC = 0.813, 95% CI 0.725–0.893) the same trend disappeared (OR = 1.08, p = 0.810). This evidence concerns the gene FNDC5 and type 2 diabetes mellitus.