*Geek Box: Measuring Insulin Sensitivity

*Geek Box: Hyperinsulinemic-euglycemic clamp & HOMA-IR

You will inevitably come across certain investigative techniques in research papers, particularly if you have an interest any condition defined by insulin resistance. The hyperinsulinemic-euglycemic clamp [HEC] is a means of assessing whole-body metabolism of glucose into peripheral tissues and the sensitivity of tissues to insulin during a steady-state of elevated glucose levels.

To perform the “clamp”, both glucose and insulin are infused [usually through a catheter in the forearm] at the same time in order to create conditions of normal plasma glucose ranges [hence ‘euglycemic’], but elevated insulin [hence ‘hyperinsulinemic’]. Under these conditions, the rate of the glucose infusion matches the rate of glucose uptake by tissues, which reflects the sensitivity of these tissues to insulin. This method has a number of strengths, particularly the assessment of total body insulin sensitivity, but also requires laboratory facilities and greater expense.

The Homeostatic Model Assessment of Insulin Resistance [HOMA-IR] is a more commonly used method due to its lower cost and ability to use at larger scale in research. HOMA-IR is a mathematical calculation based on fasting blood glucose and insulin values. As HOMA-IR is based on fasting samples, it primarily reflects hepatic insulin resistance, rather than peripheral, i.e., skeletal muscle insulin resistance [which is more demonstrable from the clamp or postprandial studies].

As a general rule in Caucasian populations, a score of 1.0 and range of 0.5-1.4 indicates normal insulin sensitivity; above 1.9 indicates early insulin resistance, while over 2.9 indicates significant insulin resistance. However, the cut-offs vary between different ethnic populations, which should be considered relative to a given study sample. HOMA-IR has a good correlation with the HEC, and the correlation is stronger in people with impaired glucose tolerance than for people with normal glucose tolerance.