How to Measure Insulin Requirements
Insulin requirements are determined using weight-based calculations, with adjustments based on diabetes type, clinical presentation, and ongoing glucose monitoring.
Initial Dose Calculation
Type 1 Diabetes
- Start with 0.5 units/kg/day as total daily dose (TDD) for metabolically stable patients 1, 2, 3
- Divide as 50% basal insulin and 50% prandial insulin (split among three meals) 1, 2
- Newly diagnosed patients typically require 0.5-1.0 units/kg/day 1
- Higher doses (up to 1.5 units/kg/day) are needed during puberty due to growth hormone and sex hormone effects 1
- Patients in the "honeymoon phase" may require as little as 0.2-0.6 units/kg/day 1
Type 2 Diabetes
- For insulin-naive patients: start with 10 units once daily OR 0.1-0.2 units/kg/day of basal insulin 1, 2, 3, 4
- For severe hyperglycemia (A1C ≥9%, glucose ≥300-350 mg/dL): start with 0.3-0.5 units/kg/day as total daily dose using basal-bolus therapy 1, 2, 3
- Augmentation therapy (adding to oral agents) typically starts at 0.3 units/kg 4
- Replacement therapy (full insulin regimen) starts at 0.6-1.0 units/kg 4
Ongoing Measurement and Titration
Basal Insulin Adjustment
- Titrate based on fasting plasma glucose (FPG) values 2, 5
- Increase by 2 units every 3 days if FPG is 140-179 mg/dL 2, 3
- Increase by 4 units every 3 days if FPG ≥180 mg/dL 2, 3
- Target FPG: 80-130 mg/dL 2, 3
- If hypoglycemia occurs, reduce dose by 10-20% immediately 2, 3
Prandial Insulin Calculation
- Use insulin-to-carbohydrate ratio (ICR): calculated as 450 ÷ TDD for rapid-acting analogs 1, 2
- Example: If TDD is 45 units, ICR = 450 ÷ 45 = 10 grams carbohydrate per 1 unit insulin 1
- Use insulin sensitivity factor (ISF): calculated as 1500 ÷ TDD 1, 2
- Example: If TDD is 50 units, ISF = 1500 ÷ 50 = 30 mg/dL reduction per 1 unit insulin 1
Critical Threshold Recognition
- When basal insulin exceeds 0.5 units/kg/day, add prandial insulin rather than continuing to escalate basal insulin alone 2, 3
- This prevents "overbasalization" which causes hypoglycemia without improving control 2, 3
- Clinical signals of overbasalization include: basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability 2, 3
Monitoring Requirements
Blood Glucose Monitoring
- Daily fasting blood glucose monitoring is essential during titration 2, 3
- Check pre-meal and 2-hour postprandial glucose to guide prandial insulin adjustments 2, 3
- For hospitalized patients: check point-of-care glucose before each meal and at bedtime 1
A1C Monitoring
- Check A1C every 3 months during intensive titration 2
- Reassess and modify therapy every 3-6 months once stable 2
Special Population Adjustments
Hospitalized Patients
- For insulin-naive or low-dose patients: start with 0.3-0.5 units/kg/day (half as basal) 3
- For patients on high-dose home insulin (≥0.6 units/kg/day): reduce TDD by 20% upon admission 3
- For high-risk patients (elderly >65 years, renal failure, poor oral intake): use 0.1-0.25 units/kg/day 3
Renal Impairment
- For CKD Stage 5 with type 2 diabetes: reduce TDD by 50% 3
- For CKD Stage 5 with type 1 diabetes: reduce TDD by 35-40% 3
Pediatric Considerations
- Infants and toddlers may require diluted insulin for precise 1-unit increments 1
- Prepubertal children generally require lower doses than adolescents 1
- Presence of ketoacidosis or steroid use dictates higher doses 1
Common Pitfalls to Avoid
- Never delay insulin initiation in patients not achieving glycemic goals with oral medications 2, 3
- Never use sliding scale insulin as monotherapy—it treats hyperglycemia reactively rather than preventing it 1, 2
- Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia 2, 3
- Never discontinue metformin when starting insulin unless contraindicated—the combination provides superior control with less weight gain 2, 3
- Never give rapid-acting insulin at bedtime as it increases nocturnal hypoglycemia risk 2, 3