How do you calculate supplemental insulin using a correction factor?

How to Calculate Supplemental (Correction) Insulin Using a Correction Factor

The correction factor (also called insulin sensitivity factor) is calculated as 1500 divided by your total daily insulin dose (TDD), and is used to determine how many mg/dL one unit of insulin will lower your blood glucose above a predetermined target. 1

Understanding the Correction Factor Formula

The correction factor tells you how much one unit of rapid-acting insulin will lower your blood glucose. Two formulas are commonly used:

• Standard formula: 1500 ÷ TDD = mg/dL drop per 1 unit of insulin 2, 1
• Alternative formula: 1700 ÷ TDD (may be used for more insulin-sensitive patients) 1

For example, if your total daily insulin dose is 50 units:

• Correction factor = 1500 ÷ 50 = 30
• This means 1 unit of rapid-acting insulin will lower your glucose by approximately 30 mg/dL 1

Calculating the Correction Dose

The correction insulin dose = (Current glucose - Target glucose) ÷ Correction factor 2

Step-by-Step Calculation:

1. Measure your current blood glucose (e.g., 250 mg/dL) 2
2. Identify your target glucose (typically 100-120 mg/dL) 2
3. Calculate the difference (250 - 100 = 150 mg/dL above target) 2
4. Divide by your correction factor (150 ÷ 30 = 5 units of correction insulin needed) 2

Critical Considerations: Insulin-On-Board

Before administering correction insulin, you must account for "insulin-on-board" (IOB) - insulin still active from previous doses - to prevent "stacking" and hypoglycemia. 2

• Rapid-acting insulin remains active for approximately 3-4 hours 2
• The pump or bolus calculator should estimate remaining active insulin and subtract this from the calculated correction dose 2
• Manual calculation: If you gave correction insulin 2 hours ago, approximately 50% may still be active 2

When to Use Correction Insulin

In Outpatient Settings:

• Before meals: Add correction insulin to your meal bolus if pre-meal glucose is above target 2
• Between meals: Use correction insulin alone for hyperglycemia, but wait at least 3-4 hours after the last rapid-acting insulin dose 2
• At bedtime: Use caution with correction doses to avoid nocturnal hypoglycemia 2

In Hospital Settings:

Correction insulin should be used in addition to scheduled basal and prandial insulin, not as monotherapy (the traditional "sliding scale" approach is ineffective and not recommended). 2

• For hospitalized patients, correction insulin should be administered every 4-6 hours using rapid-acting or regular insulin 2
• Target glucose range in non-critically ill hospitalized patients: 80-180 mg/dL 2

Adjusting Your Correction Factor

If correction doses consistently fail to bring glucose into target range, recalculate your correction factor using your current TDD - do not adjust basal insulin doses. 1

When to Reassess:

• Every 3-6 months routinely 1
• When significant changes occur in weight, activity level, or overall insulin requirements 1
• If corrections consistently overshoot (causing hypoglycemia) or undershoot (persistent hyperglycemia) 1

Pattern Recognition:

• Track post-correction glucose 2-4 hours after administering correction insulin 1
• If glucose drops too much (>50 mg/dL below target), your correction factor is too low - increase the number (use 1700 instead of 1500) 1
• If glucose remains elevated, your correction factor is too high - decrease the number or recalculate with current TDD 1

Special Populations and Situations

Insulin Pump Users:

• The pump's bolus calculator automatically applies your programmed correction factor 2
• Correction factor may vary by time of day (often need more insulin per unit in the morning due to dawn phenomenon) 2
• Approximately 40-60% of TDD should be basal delivery, with remainder as meal and correction boluses 1

Hospitalized Patients:

• For patients receiving enteral/parenteral nutrition, correction insulin should be given subcutaneously every 6 hours with regular insulin or every 4 hours with rapid-acting insulin 2
• Correction doses must be adjusted frequently based on nutritional intake 2

Patients on High-Dose Insulin:

When basal insulin exceeds 0.5 units/kg/day and glucose remains elevated, adding or intensifying prandial insulin coverage is more appropriate than relying heavily on correction doses alone. 1

Common Pitfalls to Avoid

• Never adjust basal insulin when the problem is inadequate correction dosing - these are separate components that should be adjusted independently 1
• Do not recalculate TDD daily for correction doses - TDD should be reassessed every few weeks to months, not daily 1
• Avoid "stacking" corrections by giving another dose before the previous one has finished working (wait 3-4 hours) 2
• Do not use correction insulin as monotherapy in hospitalized patients - it must be part of a scheduled basal-bolus regimen 2
• If glucose after meals is consistently out of target, adjust the carbohydrate-to-insulin ratio, not the correction factor - these parameters serve different purposes 1

Integration with Meal Insulin

When giving insulin before a meal with elevated pre-meal glucose:

Total insulin dose = Meal bolus (based on carbohydrate-to-insulin ratio) + Correction dose (based on correction factor) - Insulin-on-board 2

The correction factor works in conjunction with the carbohydrate-to-insulin ratio but should be adjusted separately based on its own effectiveness 1