Comprehensive Insulin Secretion Analysis

Insulin secretion derived from the fasting state was calculated as HOMA-B: 20·I₀/(G₀–3.5) with I₀ = fasting insulin in µU/ml and G₀ = fasting glucose in mmol/l [5] (link). All other insulin secretion indices were derived from the OGTT with insulin and C-peptide concentrations given in pmol/l, and glucose concentration given in mmol/l. AUCs of insulin, C-peptide, and glucose concentrations during the entire 120 min of the OGTT were calculated according to the trapezoid method as: 0.5·(0.5·c₀+c₃₀+c₆₀+c₉₀+0.5·c₁₂₀) with c = concentration. AUC_{Insulin(0-30)}/AUC_{Glucose(0-30)} was calculated as: (I₀+I₃₀)/(G₀+G₃₀) [9] (link). AUC_{C-Peptide(0-30)}/AUC_{Glucose(0-30)} was calculated analogously. IGI₁ was calculated as: (I₃₀–I₀)/(G₃₀–G₀) [10] (link). IGI₂ was calculated as: (I₃₀–I₀)/G₃₀[6] (link). DI oral was calculated as: IGI₁/I₀[8] (link). CIR was calculated as: 100·I₃₀/[G₃₀·(G₃₀–3.89)] [4] (link). First-phase insulin secretion was calculated as: 1283+1.829·I₃₀–138.7·G₃₀+3.772·I₀[7] (link). Insulin sensitivity derived from the OGTT was estimated as proposed by Matsuda and DeFronzo [22] (link): 10000/(G₀·I₀·G_mean·I_mean)^½. Fasting insulin clearance was calculated as CP₀/I₀ with CP₀ = fasting C-peptide, insulin clearance during the OGTT was calculated as AUC_{C-Peptide(0-120)}/AUC_{Insulin(0-120)}. Acute insulin response (AIR) derived from the IVGTT was used as gold standard for the assessment of insulin secretion and calculated as: 0.5·(0.5·I₀+I₂+I₄+I₆+I₈+0.5·I₁₀).