Assessing insulin resistance : an overview

Abstract

Insulin resistance, the condition in which there is a decreased response of target tissues to insulin is a significant predisposing factor to various metabolic abnormalities like type 2 diabetes, coronary artery disease, hypertension and dyslipidemia. It is also the common unifying mechanism in the constellation “Insulin resistance syndrome” or the metabolic syndrome whose prevalence is rising to alarming proportions. As diabetes and related disorders account for a high percentage of health cost incurred by the society, early detection of individuals at risk and appropriate intervention helps in preventing the onset of these disorders thus reducing the burden on the society. Despite a widespread awareness among clinicians about metabolic syndrome and insulin resistance, there is lack of awareness about its measurement. Hence this article discusses various methods to diagnose and quantify insulin resistance. The choice of technique to measure insulin sensitivity depend on the study objective, sample size and experimental limitation. The hyperinsulinemic euglycemic clamp technique still remains the ‘gold standard’ in measuring insulin sensitivity, as it is the most accurate index. However the cost, complexity and the required involved restricts it to highly specific metabolic studies. The ‘minimal models’ where a computer programme is used to derive insulin sensitivity from values obtained form in travenous glucose tolerance test correlates well with the clamp technique and is used much more frequently. A number of indices have been formulated form OGTT for estimating insulin sensitivity depending on the sampling intervals and has shown to have varying correlation with the clamp values. Values from OGTT also represent a true physiological state, as there is no intravenous infusion. As fasting insulin based indices such as HOMA IR and QUICKI are simple and relatively inexpensive, these are used in large-scale epidemiological studies where the end point is not necessarily insulin resistance. Himsworth in 1930s reported for the first time, a state in which there is a decreased response of target tissues to insulin. Insulin 'insensitivity' since then has been one of the most extensively investigated areas in medicine and continues to generate a great deal of research interest among clinicians and scientists around the world.