Insulin sensitivity index (ISI 0-120) from oral glucose tolerance test in healthy young adults

Abstract

Background: Insulin sensitivity (IS) is the body’s systemic responsiveness to glucose and it is the measure of the ability of endogenous insulin to reduce the glucose in extracellular fluids by inhibition of gluconeogenesis and increase peripheral glucose uptake. IS reflects on the efficiency of insulin in response to glucose intake in the body. In diabetics, IS subjects are interpreted to require smaller amounts of insulin to lower blood glucose levels than someone who has low sensitivity. There is a need to detect insulin resistance (IR) in the pre-disease state, i.e., before the onset of impaired glucose tolerance (IGT). Early detection of IR or decreased IS in healthy subjects before the onset of IGT is of importance as it facilitates implementation of preventive measures in subject with such high risk. Aims and Objectives: The objective of the study is detect early occurrence of low Insulin Sensitivity in healthy young adults, using Insulin Sensitivity Index derived from OGTT. Materials and Methods: A total of 80 healthy volunteers in the age group of 18-25 years were recruited for the study, 40 subjects were siblings of diabetics and 40 subjects were siblings of non-diabetics (SND) a standard (75 g) OGTT was performed for the study. Blood samples for determination of plasma glucose and insulin levels drawn at 0 (fasting), 30, 120 min after glucose solution ingestion. Assays of fasting (basal), 30, 120 min venous plasma glucose during OGTT was performed with glucose oxidase method on site using glucose auto analyzer. The serum plasma was stored at −20°C until assayed. Corresponding specific insulin concentration was determined using radioimmunoassay (RIA) with human specific antibody RIA kit IS was calculated using physiological OGTT based mathematical models. QUICKI was derived for fasting insulin and fasting glucose values. ISI 0-120: Uses OGTT values, using only 0 and 120 min post-glucose challenge insulin and glucose concentrations. The reference values for various IR and IS indexes for our urban population with normal OGTT (n = 79) are QUICKI = 0.31 (0.20-0.52) sibling of diabetics (SD) - 0.07, ISI 0-120 = 63.62 (27.37-134.79) SD - 22.71. We observed that SD had significantly lower IS indices ISI 0-120 (56.27, P < 0.002) and a trend toward significance for QUICKI (0.29578, P < 0.056). Results: We observed that the mathematical models ISI 0-120 to be a fairly reliable tool for assessment of IS in normoglycemic young adults, compared to QUICKI. ISI 0-120 take into consideration the all the parameters of the 2 h OGTT glucose and also includes insulin into consideration for evaluation. Simple OGTT based mathematical models can be used as a reasonable alternative to measure IS or IR instead of the cumbersome glucose clamp or other expensive techniques in epidemiological or general clinical settings. Conclusion: Detection of IR in pre-disease condition in healthy individuals, allows the physician to initiate preventive measures, such as lifestyle modification, diet and exercise, thereby preventing the high-risk subjects from progressing to disease state.