How is insulin resistance diagnosed?

Diagnosing Insulin Resistance

The most effective way to diagnose insulin resistance is through a combination of clinical evaluation for risk factors and specific laboratory tests including fasting plasma glucose, fasting insulin levels, oral glucose tolerance test (OGTT), and hemoglobin A1C. 1

Risk Assessment for Insulin Resistance

• Overweight or obesity (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans) is a significant risk factor for insulin resistance 1
• Family history of type 2 diabetes increases the risk of insulin resistance 1, 2
• Racial/ethnic predisposition (American Indian, African American, Hispanic, or Asian/Pacific Islander) should be considered when assessing risk 1, 2
• Physical signs of insulin resistance include acanthosis nigricans, hypertension, dyslipidemia, or polycystic ovary syndrome 1, 2
• Small-for-gestational-age birth weight is associated with increased risk of insulin resistance 2

Diagnostic Laboratory Tests

Primary Tests

• Fasting plasma glucose (FPG): Values between 100-125 mg/dL indicate impaired fasting glucose, suggesting insulin resistance 1, 2
• Fasting plasma insulin levels: Normal <15 mU/L, borderline high 15-20 mU/L, and high >20 mU/L 1
• Oral glucose tolerance test (OGTT): 2-hour glucose values of 140-199 mg/dL indicate impaired glucose tolerance, suggesting insulin resistance 1, 2
• Hemoglobin A1C: Values between 5.7-6.4% suggest prediabetes and potential insulin resistance 1, 2

Advanced Assessment

• QUICKI method (Quantitative Insulin Sensitivity Check Index): Calculated as the inverse of the sum of the logarithms of fasting insulin and fasting glucose; may be more sensitive than fasting insulin alone 3
• HOMA-IR (Homeostasis Model Assessment of Insulin Resistance): Correlates well with insulin resistance and doesn't significantly correlate with insulin secretion 4, 5
• Insulin-to-glucose ratio at 30 minutes during OGTT can help assess insulin secretion capacity 4

Clinical Evaluation

• Physical examination should focus on identifying:
  • Acanthosis nigricans (darkened, velvety skin patches, especially in neck folds and armpits) 1
  • Central obesity (waist circumference) 1
  • Signs of associated conditions like hypertension 1
• Laboratory assessment should include:
  • Lipid profile (particularly triglycerides, which combined with fasting insulin provides better prediction of insulin resistance) 1, 5
  • Blood pressure measurement 1

Interpretation of Results

• Impaired fasting glucose (100-125 mg/dL) indicates prediabetes and likely insulin resistance 1, 2
• Impaired glucose tolerance (2-hour OGTT 140-199 mg/dL) suggests insulin resistance 1, 2
• Elevated fasting insulin levels (>15 mU/L) directly indicate insulin resistance 1
• A combination of elevated fasting insulin and elevated triglycerides provides better sensitivity for detecting insulin resistance than either measure alone 5

Common Pitfalls and Caveats

• Testing should be performed in the fasting state to avoid postprandial variations 1
• Medications that affect glucose metabolism should be noted when interpreting results 1
• Stress hyperglycemia during acute illness can temporarily mimic insulin resistance and should not be used for diagnosis 1, 2
• In diabetic patients, there are two subpopulations: those with elevated fasting insulin (insulin resistant) and those with normal or deficient insulin levels (insulin deficient) 3
• Measuring C-peptide alongside insulin can help differentiate between endogenous insulin production and exogenous insulin administration 1