Diagnosing Insulin Resistance

Risk Assessment: Who Should Be Tested

The American Diabetes Association recommends testing for insulin resistance in patients with a BMI ≥25 kg/m² (or ≥23 kg/m² for Asian Americans) and additional risk factors 1, 2
Patients with a family history of type 2 diabetes, particularly those with a first-degree relative, should be tested for insulin resistance 1
Racial/ethnic predisposition, such as American Indian, African American, Hispanic/Latino, or Asian/Pacific Islander ancestry, increases the risk of insulin resistance 1, 2
Physical signs, including acanthosis nigricans, central/visceral adiposity, or skin tags, may indicate insulin resistance 1
Associated conditions, such as hypertension, dyslipidemia, polycystic ovary syndrome, or history of gestational diabetes, increase the risk of insulin resistance 1, 2
Lifestyle factors, including physical inactivity, contribute to the development of insulin resistance 2, 3

Fasting plasma glucose (FPG) levels between 100-125 mg/dL indicate impaired fasting glucose and insulin resistance 1, 2
Fasting insulin levels >15 mU/L directly confirm insulin resistance 1
Hemoglobin A1C (HbA1c) levels between 5.7-6.4% suggest prediabetes with underlying insulin resistance 1, 2
Oral glucose tolerance test (OGTT) with 2-hour glucose levels between 140-199 mg/dL indicates impaired glucose tolerance and insulin resistance 1, 2

Physical examination should focus on signs of insulin resistance, including acanthosis nigricans, central obesity, and lipodystrophy 1, 3
Laboratory assessment should include lipid profile, checking for dyslipidemia (HDL <35 mg/dL, triglycerides >250 mg/dL) 1, 2
C-peptide measurement can help differentiate endogenous insulin production from exogenous administration 1

Presence of impaired fasting glucose (100-125 mg/dL) or impaired glucose tolerance (2-hour OGTT 140-199 mg/dL) indicates prediabetes and likely insulin resistance 1
Elevated fasting insulin (>15 mU/L) directly confirms insulin resistance 1
HbA1c levels >6.0% indicate high risk and require aggressive intervention 2

Testing conditions should always be in a fasting state (minimum 8 hours) to avoid postprandial variations 1, 4
Normal glucose levels do not exclude insulin resistance, as hyperinsulinemia can exist with euglycemia 3
Isolated elevated C-peptide without hypoglycemia generally reflects insulin resistance rather than pathological hyperinsulinism 1

Asian Americans have increased diabetes risk at lower BMI thresholds (≥23 kg/m² vs ≥25 kg/m²) 2, 4
African Americans may have equivalent diabetes risk at BMI 26 kg/m² compared to BMI 30 kg/m² in non-Hispanic whites 2