INSULIN TOLERANCE-TESTS

Impaired sensitivity to insulin is a frequent clinical situation and i nterest in measuring sensitivity to insulin has greatly increased sinc e Reaven described the X syndrome in 1988. This syndrome is an associa tion of increased serum triglycerides, high blood pressure, low levels of HDL and insulin resistance; affected patients have an increased ri sk of coronary artery disease. Several methods have been described to measure insulin resistance. They rely on the effect of insulin on gluc ose metabolism. The euglycaemic clamp interprets the interactive feedb ack control between insulin and glucose. Insulin is infused to reach a constant serum insulin level, then glucose is administered at predete rmined levels. The blood glucose level thus corresponds to hepatic pro duction and insulin sensitivity is expressed as the amount of glucose infused in mg/kglmin. Metabolic glucose clearance is the relationship between glucose consumption and blood glucose level during the test. T his method is reliable, reproducible and eliminates the errors related to insulinindependent metabolism. Steady state plasma glucose relies on drugs which suppress endogenous insulin secretion. Glucose and insu lin are then infused at constant rates and the resulting glucose and i nsulin levels express insulin sensitivity. This method is technically difficult to handle and is used less often. Bergman's minimal model an d the modified insulin tolerance test offer other more practical and g lobal methods with particular indications. Each method has its advanta ges and disadvantages in terms of precision, cost and duration. The ch oice of a method is basically made as a function of the clinical or re search needs.