Assessment of insulin sensitivity from plasma insulin and glucose in the fasting or post oral glucose-load state

OBJECTIVE: To compare insulin sensitivity indexes derived from plasma insul in (I) and glucose (G) in the basal state (Sib) and at the second hour (I2h and G2h) of an oral glucose tolerance test (OGTT, Si2h) ii) with measureme nts of insulin sensitivity using the insulin modified frequently sampled in travenous glucose tolerance test (FSIVGTT) [Si-(IVGTT)] and (ii) with model ling of fasting glucose and insulin by the homeostasis model assessment (HO MA). SUBJECTS: 47 subjects entered the study. 31 subjects were classified as hav ing normal glucose tolerance (NGT), 10 as having impaired tolerance to gluc ose (IGT) and six as type 2 diabetes mellitus according to the World Health Organisation (WHO) criteria. MEASUREMENTS: Sib and Si2h were calculated as follows. Sib = 10(3)/(I x G x VD), Si2h = 10(3)/(I2hr x G2hr x VD) where VD is an estimate of the appare nt glucose distribution volume. A third insulin sensitivity index (SiM) was calculated by averaging Sib and Si2h. HOMA was calculated as follows: I/(2 2.5 x e(-lnG)) RESULTS: Si-(IVGTT), Sib SI2h and SiM were all significantly higher in subj ects with NGT than in those with IGT or type 2 diabetes. Si-(lVGTT) was hig hly correlated (P less than or equal to 0.0001) with the three insulin sens itivity Indexes found in the total population, in subjects with NGT and in those with IGT. In type 2 diabetic patients, a significant correlation was only noted when SiM was tested against Si-(lVGTT) (P less than or equal to 0.05) In most circumstances, the associations of Si-(IVGTT) with Sib, SI2h and SiM were stronger than the corresponding associations with Ib, I2h or H OMA. SiM was the index that correlated best with Si-(IVGTT) in the whole gr oup (r = 0.92, P < 0.0001) as well as in NGT (r = 0.86, P < 0.0001), IGT (r = 0.96; P(0.0001) and type 2 diabetes (r = 0.83, P less than or equal to 0 .05) subgroups. CONCLUSIONS: Calculations of sensitivity indexes from G and I concentration s in the basal state and during a conventional 2 h OGTT appear to be useful for coupling in the same simple and single test both a determination of gl ucose tolerance and an estimate of insulin sensitivity.