Use of Common Laboratory Tests To Identify People with Insulin Resistance

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The summary below is from the full report titled "Use of Metabolic Markers To Identify Overweight Individuals Who Are Insulin Resistant." It is in the 18 November 2003 issue of Annals of Internal Medicine (volume 139, pages 802-809). The authors are T. McLaughlin, F. Abbasi, K. Cheal, J. Chu, C. Lamendola, and G. Reaven.

What is the problem and what is known about it so far?

Insulin is a substance that the pancreas makes to help the body store energy from food. People with type 2 diabetes mellitus make plenty of insulin, but their bodies cannot use it normally, resulting in high blood sugar levels. Some people do not have type 2 diabetes but have "insulin resistance." People with insulin resistance do not have the high blood sugar levels that occur in people with type 2 diabetes, but their bodies must produce large amounts of insulin to keep sugar levels normal. Insulin resistance can lead to type 2 diabetes and heart disease. Many people with insulin resistance are overweight. Losing weight can improve insulin resistance and prevent type 2 diabetes and heart disease. Knowing whether overweight patients had insulin resistance could help doctors tell who would benefit most from weight loss. Unfortunately, the standard testing for insulin resistance is a complicated laboratory procedure.

Why did the researchers do this particular study?

To see how well common tests can identify patients with insulin resistance.

Who was studied?

258 overweight volunteers who had participated in the researchers' previous studies and had normal blood pressure and no diabetes.

How was the study done?

The researchers had completed standard testing for insulin resistance in the study patients, so they knew who had insulin resistance. The researchers also had information on the patients' body mass index (a measure of body size that considers weight and height) and blood tests for levels of sugar, insulin, and lipids. The lipid tests included total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride levels. The researchers saw how well each of the following measures predicted insulin resistance: ratio of triglyceride to HDL cholesterol, triglyceride level, insulin level, ratio of total cholesterol to HDL cholesterol, body mass index, HDL cholesterol level, glucose level, and total cholesterol level.

What did the researchers find?

The tests that were most useful for identifying patients who had insulin resistance were triglyceride level, ratio of triglyceride to HDL cholesterol, and insulin level. However, no test was perfect and all tests missed some people with insulin resistance and incorrectly labeled some people as insulin resistant when they were not. In addition, insulin levels are not standardized across laboratories, so similar values obtained from another laboratory might or might not indicate insulin resistance. For this reason, the authors favor the lipid markers (triglyceride level and the ratio of triglyceride to HDL cholesterol) of insulin resistance.

What were the limitations of the study?

This study involved research volunteers, so the results might not apply to overweight people in general. More important, this study does not prove that directing weight loss effort according to levels of triglycerides and HDL cholesterol would actually decrease the development of type 2 diabetes and heart disease among overweight people.

What are the implications of the study?

Since it is easy to measure triglyceride and HDL cholesterol levels, doctors might consider using these tests to predict whether their overweight patients are likely to have insulin resistance. However, further study is needed to know whether such testing of overweight people is a good strategy for decreasing the development of type 2 diabetes and heart disease.