To date, there is no commonly used test for diagnosing insulin resistance. There are sophisticated tests, such as the euglycemic clamp, that can give a precise answer as to whether or not a person has insulin resistance. These tests are expensive and complicated and are not widely used except in research. 

Instead, physicians are more likely to order simpler tests that can give indirect evidence of insulin resistance. These tests may be administered to patients with high risk factors. The most common tests are:

• Fasting glucose test. Measures blood glucose after a person has gone overnight without eating. Patients with readings between 100 and 125 milligrams per deciliter (mg/dL) have blood glucose measurements that are above normal, but not high enough to be considered diabetes. This is diagnosed as impaired fasting glucose  (prediabetes), and frequently indicates a history of insulin resistance likely to eventually trigger diabetes.
  
  
• Oral glucose tolerance test (OGTT). Measures blood glucose up to four hours after the patient consumes a sweet liquid made up of glucose. If blood glucose increases to a level between 140 mg/dL and 199 mg/dL, the patient is diagnosed as having a prediabetic condition known as impaired glucose tolerance (also called prediabetes). This indicates a history of insulin resistance likely to eventually trigger diabetes. Patients scheduled to take a glucose tolerance test must fast the night before the test after consuming a carbohydrate-rich diet for three days.

In addition, a fasting insulin test and a C peptide test may indicate hyperinsulinemia. For men, a testosterone blood test may indicate low testosterone (hypogonadism), which contributes to sexual dysfunction and may be a risk factor for insulin resistance.

Recent research has found increased bloodstream levels of a substance known as retinol-binding protein 4 (RBP4) in people with insulin resistance. Scientists say the discovery may lead to improved diagnosis and treatment.