The most widely used biochemical diagnostic criteria of endogenous hyperinsulinemic hypoglycemia are as follows: insulin level ≥ 3 μIU/l, C-peptide level ≥ 0.6 ng/ml, and proinsulin level ≥ 5 pmol/l with end-of-fast glucose ≤ 3.0 mmol/l (4, 6–8). This evidence concerns the gene INS and hyperinsulinemic hypoglycemia.