Insulin Resistance

Tests
There is no one test that can directly detect insulin resistance. Instead, a doctor will look at a patient’s entire clinical picture and may suspect that the patient has insulin resistance if he has increased blood glucose levels, increased levels of triglycerides and LDL cholesterol, and decreased concentrations of HDL cholesterol. Laboratory tests most likely to be ordered include:

• Glucose. This is usually performed fasting but, in some cases, a doctor may also request a GTT (glucose tolerance test – two glucose tests that are taken before and 120 minutes after a glucose challenge). The goal of glucose testing is to determine whether a patient has an impaired response to glucose i.e. whether the blood glucose level climbs higher than it should under normal circumstances.
• Lipid profile. This measures the HDL, LDL, triglycerides, and total cholesterol. If the triglycerides are significantly elevated, a DLDL (direct measurement of the LDL) may need to be done.

Other laboratory tests that may be used to help evaluate insulin resistance and provide additional information include:

• Insulin. The fasting insulin test is variable, but insulin levels will usually be elevated in those with significant insulin resistance.
• hs-CRP. This is a measure of low levels of inflammation that may be done as part of an evaluation of cardiac risk. It may be increased with insulin resistance. Mild inflammation is a feature of metabolic syndrome.
• sdLDL. This is a measurement of the number of small dense low-density lipoprotein molecules a patient has. This test is not ordered frequently but may be measured as part of a lipoprotein subfractions test.
• Insulin tolerance test (ITT). Not widely used but is one method for determining insulin sensitivity (or resistance), especially in obese individuals and those with PCOS. This test involves an IV-infusion of insulin, with subsequent measurements of glucose and insulin levels.

Specific insulin suppression tests may also be requested in a research setting to study insulin resistance but are not generally used in a clinical setting. An intravenous glucose tolerance test can be carried out where the glucose load is given into a vein rather than by mouth but again this test tends to be used for research purposes only rather than in a clinical setting.