Insulin Level Testing in Pediatrics
Insulin Testing in Pediatrics
Insulin testing is crucial for evaluating disorders of glucose homeostasis, hypoglycemia, and insulin resistance in children. Understanding proper testing conditions and interpretation is essential for accurate diagnosis.
Key Points
- Insulin secretion is pulsatile and glucose-dependent
- Fasting samples are more reliable than random samples
- C-peptide levels should be measured concurrently
- Multiple factors affect insulin sensitivity
Basic Testing Approaches
Fasting Tests
- Standard Measurements:
- Fasting insulin
- Fasting glucose
- C-peptide
- Proinsulin (in special cases)
- Duration of Fast:
- Infants: 4-6 hours
- Children: 8-12 hours
- Adolescents: 8-14 hours
Calculated Indices
- HOMA-IR (Homeostatic Model Assessment of Insulin Resistance)
- Formula: (Fasting Insulin × Fasting Glucose)/22.5
- Most commonly used in research
- Age-specific cutoffs apply
- QUICKI (Quantitative Insulin Sensitivity Check Index)
- Formula: 1/(log[fasting insulin] + log[fasting glucose])
- Better correlation with glucose clamp studies
Dynamic Testing Protocols
Oral Glucose Tolerance Test (OGTT)
- Procedure:
- Glucose load: 1.75g/kg (max 75g)
- Sampling times: 0, 30, 60, 90, 120 minutes
- Measure both glucose and insulin
- Indications:
- Suspected insulin resistance
- Prediabetes evaluation
- Type 2 diabetes screening
Mixed Meal Test
- Protocol:
- Standardized meal (complex carbs, protein, fat)
- Sampling at 0, 30, 60, 90, 120 minutes
- More physiologic than OGTT
- Applications:
- Evaluation of postprandial hypoglycemia
- Assessment of insulin secretion
- Beta cell function testing
Reference Ranges and Interpretation
Fasting Insulin Levels
- Prepubertal Children:
- Normal: 2-13 μU/mL
- Borderline: 13-20 μU/mL
- Elevated: >20 μU/mL
- Adolescents:
- Normal: 2-17 μU/mL
- Borderline: 17-25 μU/mL
- Elevated: >25 μU/mL
OGTT Insulin Response
- Normal Response:
- Peak: <100 μU/mL
- 2-hour: <75 μU/mL
- Insulin Resistance Pattern:
- Peak: >150 μU/mL
- 2-hour: >75 μU/mL
- Delayed return to baseline
Clinical Applications
Hypoglycemia Evaluation
- Critical Samples:
- Glucose <50 mg/dL
- Insulin
- C-peptide
- Beta-hydroxybutyrate
- Free fatty acids
- Diagnostic Ratios:
- Insulin/Glucose ratio
- C-peptide/Glucose ratio
Insulin Resistance Assessment
- High-Risk Groups:
- Obesity
- Acanthosis nigricans
- Family history of T2DM
- PCOS in adolescents
- Monitoring Parameters:
- Fasting insulin trends
- HOMA-IR changes
- HbA1c
- Lipid profile
Special Considerations and Pitfalls
Pre-analytical Factors
- Sample Handling:
- Process within 24 hours
- Separate serum promptly
- Avoid hemolysis
- Patient Preparation:
- Appropriate fasting duration
- No acute illness
- Medication considerations
Interfering Factors
- Physiological:
- Puberty (insulin resistance)
- Growth hormone excess
- Stress/illness
- Exercise
- Medications:
- Glucocorticoids
- Growth hormone
- Beta-blockers
- Antipsychotics
