There is no one test that can directly detect insulin resistance. Instead, a health practitioner will look at an individual's entire clinical picture and may suspect insulin resistance if the person has increased 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 health practitioner may also order a GTT (glucose tolerance test, several glucose tests that are taken before and at timed intervals after a glucose challenge). The goal of glucose testing is to determine whether a patient has an impaired response to glucose.
- A1c. This test reflects average blood glucose levels over the past 3 months by measuring the percentage of hemoglobin that have been glycated, or bound with glucose, in the bloodstream. It is also called hemoglobin A1c, HbA1c, or a glycohemoglobin test.
- 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.
- One of the most common ways of detecting insulin resistance is by using the homeostatic model assessment (HOMA). It involves measuring glucose and insulin levels and then using a calculation to estimate function of the beta cells in the pancreas that produce insulin and insulin sensitivity.
Other laboratory tests that may be ordered 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.
- LDL-P. This is a measurement of the number of various types of low-density lipoprotein particles using a lipoprotein subfractions test. It is thought that a greater number of small, dense LDL particles than large, fluffy particles is associated with a greater risk of cardiovascular disease.
- Insulin tolerance test (ITT). This test is 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.
- Quantitative insulin sensitivity check index (QUICKI). This uses a mathematical formula to calculate a number based on glucose and insulin blood tests. Insulin resistance is diagnosed based on where the calculated value lies in the QUICKI index.
Specific insulin suppression tests may also be ordered in a research setting to study insulin resistance but are not generally used in a clinical setting.