INS and Hypoglycemia: Biochemical assessment: Symptoms and/or signs suggesting hypoglycemia combined with a ≤55 mg/dL (3.0 mmol/L) plasma glucose, a ≥3.0 μU/mL (18 pmol/L) plasma insulin, a ≥0.6 ng/mL (0.2 nmol/L) C-peptide, and a ≥5.0 pmol/L proinsulin indicate endogenous hyperinsulinism [227, 228, 231].