To investigate this question we studied the association of fasting, 30 and 120 min proinsulin levels and proinsulin area under the curve (AUC) in an oral glucose tolerance test (OGTT) with the worsening of hyperglycemia and incident type 2 diabetes in a 6-year prospective follow-up of the METSIM cohort. Here, INS is linked to type 2 diabetes mellitus.