Correction Factor (Insulin Sensitivity Factor) for Adults
For an adult without renal or hepatic impairment, the correction factor (insulin sensitivity factor) is calculated as 1500 ÷ total daily dose (TDD) of insulin, indicating how much 1 unit of rapid-acting insulin will lower blood glucose in mg/dL. 1
Calculating the Correction Factor
The correction factor tells you how many mg/dL one unit of rapid-acting insulin will drop the blood glucose level 1. The standard formula is:
- Correction Factor = 1500 ÷ Total Daily Dose (TDD) 1, 2
- Alternative formula: 1700 ÷ TDD for some rapid-acting analogs 1
For example, if a patient uses 50 units of insulin per day total, their correction factor would be 1500 ÷ 50 = 30 mg/dL per unit 1. This means each unit of rapid-acting insulin should lower their blood glucose by approximately 30 mg/dL 1.
Applying the Correction Factor
To calculate the correction dose, subtract your target blood glucose from your current blood glucose, then divide by your correction factor 3, 1:
- Correction Dose = (Current BG − Target BG) ÷ Correction Factor 1
Using the example from the guidelines: if blood glucose is 250 mg/dL, target is 125 mg/dL, and correction factor is 25, then: (250 − 125) ÷ 25 = 5 units of rapid-acting insulin 3.
Relationship to Other Insulin Parameters
The correction factor has a highly predictable relationship to the insulin-to-carbohydrate ratio: CF = ICR × 4.5 1, 2. This means if your carb ratio is 1:10 (1 unit per 10 grams), your correction factor should be approximately 45 mg/dL per unit 1, 2.
Important Timing Considerations
- Administer rapid-acting correction insulin 0–15 minutes before meals for optimal effect 1
- Never give rapid-acting insulin at bedtime as a sole correction dose, as this markedly increases nocturnal hypoglycemia risk 1
- Account for "insulin on board" from previous boluses to avoid insulin stacking and hypoglycemia 1
When to Reassess Your Correction Factor
The correction factor requires periodic reassessment as insulin requirements change with weight, exercise patterns, and other physiological factors 1. Specifically:
- Recalculate when total daily insulin dose changes significantly 1
- Reassess if correction doses consistently fail to bring glucose into target range 1
- Re-evaluate during illness, changes in activity level, or weight changes 1
- Consider reassessment after at least 1–2 weeks of stable therapy 1
Common Pitfalls to Avoid
- Not accounting for insulin on board leads to insulin stacking and hypoglycemia 1
- Using a fixed correction factor throughout the day ignores diurnal variations in insulin sensitivity, though most patients can use a single factor 1
- Failing to adjust the correction factor when total daily dose changes results in suboptimal glucose control 1
- Overestimating correction needs by not waiting for previous insulin doses to finish working (rapid-acting insulin has a 3–5 hour duration) 1