Insulin Resistance Detection and Diagnosis

Introduction to Insulin Resistance Testing

The American Diabetes Association recommends using the oral glucose tolerance test (OGTT) with 2-hour glucose values as the most sensitive test for early detection of insulin resistance before fasting abnormalities appear, especially in adults with BMI >25 1.
The American Diabetes Association suggests starting with fasting plasma glucose (FPG) as the initial screening test because it is convenient, inexpensive, reproducible, and widely available, although it primarily detects diabetes rather than early insulin resistance 2, 3.

The American Diabetes Association indicates that FPG ≥126 mg/dL confirms diabetes, requiring confirmation on a separate day 3, 4.
The American Diabetes Association suggests that FPG 100-125 mg/dL indicates impaired fasting glucose (IFG), suggesting insulin resistance 3, 4.
Normal FPG does not exclude insulin resistance, according to the American College of Endocrinology 1.
The American Diabetes Association recommends that 2-hour glucose 140-199 mg/dL during an OGTT indicates impaired glucose tolerance (IGT), representing early insulin resistance 3, 1.
The American Diabetes Association states that 2-hour glucose ≥200 mg/dL during an OGTT confirms diabetes 3, 4.

The American Heart Association advises testing in the true fasting state (minimum 8 hours without caloric intake) to avoid postprandial variations that invalidate results 1, 3.
For Asian Americans, the American Diabetes Association recommends using the lower BMI threshold of ≥23 kg/m² rather than ≥25 kg/m² when determining who needs testing, as they have equivalent diabetes risk at lower BMI values 4, 5, 1.

The American College of Endocrinology suggests using FPG for routine screening in asymptomatic adults with BMI ≥25 kg/m² and additional risk factors 3, 4, 5.
The American Diabetes Association recommends using OGTT when FPG is normal but clinical suspicion for insulin resistance remains high based on physical signs or metabolic abnormalities 2, 1.
The American College of Endocrinology advises measuring fasting insulin directly when definitive confirmation of insulin resistance is needed in patients with borderline glucose values or when considering insulin-sensitizing therapy 1.
The American Diabetes Association considers HbA1c (≥5.7%) as an alternative screening test that doesn't require fasting, though it is less sensitive for early insulin resistance than OGTT 4, 1.