ABSTRACT
Clinically, a number of techniques have been developed to detect the presence of insulin resistance and
assessments vary in complexity and precision (Figure 2.2)2-6. However, from a clinical perspective, the most practical way of assessing insulin resistance is the measurement of plasma insulin levels. (Insulin is produced in pancreatic β-cells and is released into the bloodstream in response to stimulation that occurs after a meal ingestion (Figures 2.3 and 2.4)7. As type 2 diabetes is characterized by an antecedent phase of insulin resistance that requires a compensatory increase in insulin secretion to maintain euglycemia, an elevated insulin level in the fasting state is indicative of insulin resistance.) It is suggested that this be performed in the overnight fasting condition, since in the postprandial state glucose levels are changing rapidly, and variable levels of glucose confound the simultaneous measurement of insulin. The homeostasis model assessment (HOMA)4,5 of insulin sensitivity is a simple, inexpensive alternative to more sophisticated techniques and derives an estimate of insulin sensitivity from the mathematical modeling of fasting plasma glucose and insulin concentrations. Specifically, an estimate of insulin resistance by HOMA score is calculated with the formula: (fasting serum insulin (μU/ml) × fasting plasma glucose (mM))/22.5. Oral glucose tolerance testing (OGTT) enables the insulin secretory response to an oral glucose challenge to be calculated6. The frequently sampled intravenous glucose tolerance test (FSIVGTT) is a method that is less invasive and more practical than the euglycemic hyperinsulinemic clamp technique and one that can be applied to larger populations2,3. With this procedure, glucose is injected as a bolus, and both glucose and insulin levels are assessed frequently from an
indwelling catheter over the next several hours. The results are entered in a computer model that generates a value as an index of insulin sensitivity, termed SI units.
