What is the HOMO (Homeostatic Model Assessment) IR (Insulin Resistance) test?

HOMA-IR Test: A Surrogate Measure for Insulin Resistance

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is a validated mathematical model that serves as a surrogate estimate of insulin resistance using fasting glucose and insulin levels, calculated as: (fasting insulin [mU/ml] × fasting glucose [mmol/L])/22.5. 1

How HOMA-IR Works

HOMA-IR provides a simple method to assess insulin resistance from a single fasting blood sample, making it more practical than more complex and invasive procedures like the euglycemic clamp test.

Calculation Method:

• Formula: HOMA-IR = (fasting insulin [mU/ml] × fasting glucose [mmol/L])/22.5 1, 2
• Requires only a single plasma sample for insulin and glucose measurements
• Higher values indicate greater insulin resistance

Clinical Applications:

1. Screening for insulin resistance in patients with:

   • Metabolic syndrome risk factors
   • Non-alcoholic fatty liver disease (NAFLD)
   • Polycystic ovary syndrome
   • Obesity or abnormal fat distribution

2. Monitoring metabolic health:

   • Following weight loss interventions 1
   • Assessing progression of metabolic diseases
   • Evaluating response to insulin-sensitizing therapies

Interpretation and Limitations

Interpretation:

• Normal range: Values vary by population, but generally:
  • <1.0: Normal insulin sensitivity
  • 1.0-2.5: Moderate insulin resistance

  • 2.5: Significant insulin resistance 3

• Cut-off values may need adjustment based on BMI category, with higher thresholds needed for those with higher BMI 3

Important Limitations:

1. Not validated for all populations:

   • Limited accuracy in patients with type 2 diabetes on insulin therapy 4
   • May not accurately reflect insulin resistance in individuals with impaired beta-cell function 5
   • Different cut-offs may be needed across BMI categories 3

2. Technical considerations:

   • Insulin assays vary widely between laboratories, affecting results 1
   • No universally agreed threshold defining insulin resistance 1
   • Pre-analytical errors in glucose measurement can affect results 6

3. Reduced sensitivity to detect changes:

   • May not reliably detect diet-induced changes in insulin resistance 5
   • Less accurate when pancreatic function is compromised 5

Clinical Recommendations

• HOMA-IR provides a surrogate estimate of IR in persons without diabetes and can be recommended when proper reference values have been established 1

• For diagnostic purposes:

  • Use HOMA-IR to confirm altered insulin sensitivity in cases of diagnostic uncertainty (e.g., ultrasound-defined steatosis with normal body weight) 1
  • Consider using HbA1c-derived estimated average glucose as an alternative to fasting glucose for HOMA-IR calculation when fasting samples are difficult to obtain 6

• For monitoring:

  • HOMA-IR may help identify patients at risk of NASH or fibrosis progression in selected cases 1
  • Improvement in HOMA-IR during weight loss may indicate beneficial metabolic improvement for NAFLD 1

Alternative Approaches

• Gold standard methods for measuring insulin resistance:

  • Hyperinsulinemic-euglycemic clamp
  • Minimal model analysis of intravenous glucose tolerance test

• Alternative surrogate markers:

  • HOMA2-IR (updated computerized model)
  • QUICKI (Quantitative Insulin Sensitivity Check Index)
  • Matsuda Index (requires oral glucose tolerance test)

Practical Considerations

• Fasting for at least 8 hours is required for accurate results
• Morning sampling is preferred to minimize diurnal variation
• Results should be interpreted in clinical context, considering other metabolic parameters
• Regular monitoring may be more valuable than a single measurement

Remember that while HOMA-IR is a useful tool for estimating insulin resistance in research and clinical settings, its limitations should be considered when making clinical decisions, especially in patients with compromised pancreatic function or those on insulin therapy.