Methods for Measuring Insulin Sensitivity

Overview

Patients with high blood pressure, diabetes, and who are overweight are known to have defects in the way their body responds to insulin. The purpose of this study is to develop better methods for measuring the way body tissue responds to insulin and sugar (glucose). Researchers are planning to study four groups of patients. 1. Normal volunteers 2. Patients who have mild to moderate high blood pressure 3. Patients who are overweight 4. Patients who have mild to moderate diabetes controlled with oral medication In this study patients and volunteers will undergo two separate tests designed to determine how well insulin is working in the body. The first test is called a glucose clamp test. Patients will have two needles placed in the veins of their arms. One needle will be used to take blood samples, the other needle will be used to inject doses of sugar (glucose) and insulin. The second test is called the frequently sample intravenous glucose tolerance test. In this test patients will have sugar (glucose) injected into their veins followed by a slow injected dose (infusion) of insulin. Researchers will periodically take blood samples during the test. Patients participating in the study will not directly benefit from it. However, the information gained from this study may be useful for improving the diagnosis and therapy of diseases such as diabetes, obesity, and high blood pressure (hypertension).

We hypothesize that the majority of the information needed to accurately estimate insulin sensitivity is contained in the fasting insulin and glucose levels as well as the insulin and glucose levels obtained shortly after an intravenous glucose load. We propose to test this hypothesis by performing both hyperinsulinemic euglycemic glucose clamps as well as intravenous glucose tolerance tests on normal volunteers and groups of patients with diabetes, hypertension, or obesity (diseases known to be associated with insulin resistance). Data from these studies will be used obtain estimates of insulin sensitivity by the glucose clamp method, minimal model method, and a novel analysis that utilizes only fasting and peak levels of glucose and insulin. We hope to devise a simpler method for determining insulin sensitivity in vivo that is suitable for testing large populations. This method will require only a few blood samples, take less than one hour to perform, and correlate with glucose clamp estimates at least as well as the minimal model method.