From the Guidelines
Diagnosing insulin resistance typically involves a combination of clinical assessment, blood tests, and sometimes specialized testing, with the most recent guidelines recommending screening for prediabetes and type 2 diabetes risk through an informal assessment of risk factors or with an assessment tool, such as the ADA risk test 1. To diagnose insulin resistance, your doctor will likely start with a fasting blood glucose test and hemoglobin A1C to check your blood sugar levels.
Diagnostic Criteria
The diagnostic criteria for prediabetes, which is often a sign of insulin resistance, include:
- Fasting plasma glucose (FPG) of 100 mg/dL (5.6 mmol/L) to 125 mg/dL (6.9 mmol/L)
- 2-hour plasma glucose (2-h PG) during a 75-g oral glucose tolerance test (OGTT) of 140 mg/dL (7.8 mmol/L) to 199 mg/dL (11.0 mmol/L)
- A1C of 5.7–6.4% (39–47 mmol/mol) 1 A fasting insulin test may also be ordered to directly measure insulin levels.
Specialized Testing
The gold standard for diagnosis is the hyperinsulinemic-euglycemic clamp, though this complex procedure is rarely used in clinical practice. More commonly, doctors use the HOMA-IR (Homeostatic Model Assessment for Insulin Resistance) calculation, which uses fasting glucose and insulin levels. Physical signs that might prompt testing include acanthosis nigricans (darkened skin patches), central obesity, and high blood pressure. Risk factors like family history of diabetes, sedentary lifestyle, and certain medications can also suggest the need for testing. Your doctor may also check for related conditions like high triglycerides, low HDL cholesterol, and elevated liver enzymes. Insulin resistance develops when cells become less responsive to insulin, requiring the pancreas to produce more insulin to maintain normal blood sugar levels, which eventually can lead to type 2 diabetes if left unaddressed. In children, fasting plasma glucose testing has been recommended for those at risk for the presence or development of type II diabetes, including those who are overweight, have a family history of type II diabetes, or have signs of insulin resistance or conditions associated with insulin resistance 1.
From the Research
Diagnosing Insulin Resistance
To diagnose insulin resistance, several methods can be employed, including:
- Oral glucose tolerance test (OGTT) to estimate insulin secretion and insulin resistance 2
- Insulin tolerance test to measure the decline of plasma glucose after the injection of a bolus of insulin 2
- Homeostasis model assessment (HOMA) to estimate relative insulin resistance 2, 3, 4
- Fasting insulin, proinsulin, or split proinsulin concentrations to estimate insulin resistance 2
- Quantitative insulin sensitivity check index (QUICKI) and McAuley indexes to predict insulin sensitivity or insulin resistance 5
Methods for Estimating Insulin Resistance
The following methods can be used to estimate insulin resistance:
- Fasting plasma glucose level of 12 mU/l or higher 5
- Homeostasis model assessment of 2.6 or higher 5
- Minimal model approximation of the metabolism of glucose (MMAMG) S(i) value of 21 or lower 5
- QUICKI of 0.33 or lower 5
- McAuley index of 5.8 or lower 5
Oral Glucose Tolerance Test
The OGTT can be used to evaluate both insulin release and insulin sensitivity in subjects with normal and abnormal glucose tolerance 3, 4
- The test involves measuring glucose and insulin concentrations at 0,60, and 120 minutes after oral glucose loading 4
- The value 1/HOMA can be used as an index of insulin sensitivity, and deltaI/deltaG at 60 minutes can be used as an index of insulin release 4
Limitations of Measuring Insulin Levels
Measuring serum insulin concentrations is not a reliable method for diagnosing insulin resistance, as insulin levels can be influenced by various factors 6
- Fasting serum insulin levels should be reserved for large population-based epidemiological studies, where they can provide valuable data on the relationship of insulin sensitivity to risk factors for diabetes and cardiovascular disease 6