INS and type 2 diabetes mellitus: It is possible that metabolites could further improve the predictive value of diabetic subgroups, because we have recently shown that type 2 diabetes can be subdivided into five subgroups with six clustering variables (age at diagnosis, BMI, HbA1c, GAD autoantibodies, homeostatic model assessment of β-cell function, and homeostatic model assessment of INS resistance) with C-peptide measurements (34).