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Metabolic Markers May Help Identify Insulin Resistance in Overweight Individuals

Easily measured metabolic markers may be useful for identifying overweight individuals who are insulin resistant and likely to benefit from weight loss counselling, according to a recent American study.

Insulin resistance is an independent predictor for both type 2 diabetes and cardiovascular disease (CVD), and it has been shown to occur more frequently in overweight individuals. Although weight loss can significantly decrease insulin resistance and the associated health risks, many physicians do not provide weight loss counselling for overweight patients.

"Reluctance to assign weight control programs a high priority might be decreased if identifying overweight or obese individuals at greatest risk were possible," writes Tracey McLaughlin, MD, of Stanford University School of Medicine, California. However, detection of insulin resistance by direct measurement of insulin-mediated glucose disposal is often not clinically practical.

To address this concern, Dr. McLaughlin and colleagues evaluated the ability of several metabolic markers to identify overweight individuals who are both insulin resistant and at greatest risk for CVD.

Metabolic markers were measured in 258 overweight or obese nondiabetic individuals (mean age, 50 years; 127 men) and statistically evaluated for associations with insulin resistance, estimated by a modified insulin suppression test.

Of the 8 markers analysed in the study, insulin concentration, plasma triglyceride concentration, and the ratio of triglyceride to high-density lipoprotein (HDL) cholesterol concentrations were found to be 3 most useful for identifying insulin resistance. The sensitivity of the markers was 67%, 64%, and 57% for triglycerides, triglyceride-HDL cholesterol ratio, and insulin, respectively, and specificities were 71%, 68%, and 85%.

According to Dr. McLaughlin, the optimal cut-off values for identifying insulin resistance were 1.47 mmol/L for triglycerides, 1.8 in SI units for triglyceride-HDL ratio, and 109 pmol/L for insulin.

Although plasma insulin was found to be the marker most closely associated with insulin resistance, the researchers note that, "the absence of a standardized insulin assay significantly hampers the clinical utility of plasma insulin."

However, they emphasise that both plasma triglyceride and triglyceride-HDL cholesterol ratio gave specificity and sensitivity similar to the Adult Treatment Panel III criteria proposed to diagnose the metabolic syndrome (sensitivity, 52%; specificity, 85%). Both markers are additionally known to be associated with an increased risk for cardiovascular disease.

"The relatively more consistent association between low HDL cholesterol level and CVD makes the triglyceride-HDL cholesterol ratio a clinically appealing marker for CVD risk in addition to insulin resistance," the researchers conclude.

Ann Intern Med 2003 Nov 18;139:10:802-9. "Use of metabolic markers to identify overweight individuals who are insulin resistant"

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