Diabetes Correction Factor Checking and Calculation

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The insulin correction factor (also known as insulin sensitivity factor or ISF) indicates how much mg/dl (or mmol/l) one unit (IU) of rapid-acting or regular insulin lowers your blood glucose.

Important Medical Notice:

The following information and tools are intended solely for general informational, educational, and documentation purposes. They do not constitute medical advice, diagnosis, or treatment recommendations and under no circumstances replace individual consultation, examination, or care by qualified medical professionals (diabetologist/physician). Dose adjustments or changes to insulin therapy should always be discussed with your treating diabetes care team.

Below, we compare the values using two common examples:

• mg/dl (1800 Rule): 50 mg/dl per 1 IU
• mmol/l (100 Rule): 2.8 mmol/l per 1 IU

1. Basic Principle & Both Rules in Comparison

Both the 1800 Rule (for mg/dl) and the 100 Rule (for mmol/l) are medical rules of thumb used in diabetology. They estimate your personal correction factor based on your total daily insulin dose.

Where Do the Numbers 1800 and 100 Come From?

Both rules are based on empirical clinical studies and link your Total Daily Dose (TDD) of insulin directly to your blood glucose reduction:

Feature	1800 Rule (for mg/dl)	100 Rule (for mmol/l)
Unit	mg/dl	mmol/l
Formula	Correction Factor = 1800 / Total Daily Dose	Correction Factor = 100 / Total Daily Dose
Example (at TDD = 36 IU)	1800 / 36 = 50 mg/dl per 1 IU	100 / 36 = 2.8 mmol/l per 1 IU

2. Excursus: What is the Total Daily Dose (TDD) & Special Considerations for Premixed Insulin?

What is Total Daily Dose (TDD)?

The TDD is the sum of all insulin units injected within a 24-hour period. It consists of:

$$\text{TDD} = \text{Basal Insulin (Long-acting)} + \text{Bolus Insulin (All mealtime insulin combined)}$$

• Example: 15 IU Basal + 21 IU Meal Boli (6+7+8 IU) = 36 IU TDD. To determine this value, it is best to calculate the average of the last 3 to 7 days.

Special Considerations for Premixed Insulin (Mix-Insulin)

• TDD Calculation: For premixed insulin, simply add up all daily doses (e.g., 22 IU in the morning + 14 IU in the evening = 36 IU TDD).
• No Spontaneous Correction with Premixed Insulin: Because premixed insulin always contains a intermediate/long-acting basal component, it must not be injected spontaneously to correct high blood sugar. Doing so would inadvertently inject extra long-acting insulin, leading to delayed hypoglycemia. Corrections should be managed in consultation with your physician, either by adjusting mealtime doses or by using a separate, pure rapid-acting insulin.

3. Practical Determination System (The 3-Day Screening)

Because insulin sensitivity varies throughout the day (often higher resistance in the morning due to hormones like cortisol, higher sensitivity in the evening), a single test is usually not sufficient.

During a 3-Day Screening, you perform the correction test on different days at different times of day. To rule out random outliers, a confirmation test on a subsequent day (24 hours later) is recommended for each time slot.

[Day 1: MORNING]    --> Test immediately after waking up (before breakfast)
[Day 2: MIDDAY]     --> Test before lunch (at least 4 hours after breakfast bolus)
[Day 3: EVENING]    --> Test before dinner (at least 4 hours after lunch bolus)

Requirements Before EVERY Test Run

• No Active Insulin: At least 3 to 4 hours must have passed since the last meal and last mealtime/correction bolus.
• Fasting During the Test: Drink only water or unsweetened tea for 3 to 4 hours during the test; do not eat.
• No Physical Activity: Avoid exercise, heavy lifting, or strenuous walking.
• No Confounding Factors: No stress, illness/fever, alcohol consumption the night before, or severe hypoglycemia within the last 24 hours.
• Baseline Value: Blood glucose should be slightly elevated (e.g., 180–220 mg/dl / 10–12 mmol/l) to allow for a controlled drop.

Step-by-Step Procedure for Each Test Slot

[1. Measure Start BG]  -->  [2. Inject EXACTLY 1 IU]  -->  [3. Wait 3-4 Hours]  -->  [4. Measure End BG & Calculate Drop]

Important Safety Rule During Testing:

During the test screening, always inject exactly 1 IU of insulin – regardless of how high your starting value is. Do not attempt to correct directly to a target value (e.g., 100 mg/dl) during testing. This prevents hypoglycemia and gives you an accurate measurement of the effect of 1 IU!

1. Measure Start Value (Start BG):
   • mg/dl: e.g., 210 mg/dl
   • mmol/l: e.g., 11.8 mmol/l
2. Inject Exactly 1 IU of Correction Insulin:Inject exactly 1 IU of your usual rapid-acting insulin.
3. Wait for Full Action (3–4 Hours):Do not eat or perform physical activity.
4. Measure End Value (End BG):
   • mg/dl: e.g., 160 mg/dl
   • mmol/l: e.g., 9.0 mmol/l
5. Calculate the Difference:Correction Factor = Start BG – End BG
   • mg/dl: 210 – 160 = 50 mg/dl per 1 IU
   • mmol/l: 11.8 – 9.0 = 2.8 mmol/l per 1 IU

4. The Formula for Everyday Corrections

Only after completing the screening and establishing your time-of-day correction factors should you apply them for everyday corrections:

Unit	Formula	Practical Example
mg/dl (Factor 50)	Dose (IU) = (Current BG – Target BG) / 50	Current: 250, Target: 100 -> (250 – 100) / 50 = 150 / 50 = 3 IU
mmol/l (Factor 2.8)	Dose (IU) = (Current BG – Target BG) / 2.8	Current: 14.0, Target: 5.6 -> (14.0 – 5.6) / 2.8 = 8.4 / 2.8 = 3 IU

5. Excel Spreadsheet Template

For easy tracking and automatic calculation, a pre-built Excel template is available:

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Excel File Structure & Features:

• Tab 1 – “Instructions & Rules”:
  Reference guide containing all requirements, criteria, and guidelines at a glance. No data input required.
• Tab 2 – “3-Day-Screening” (Logbook):
  • Data Entry: Simply enter Date, Start BG, Dose (always 1 IU), Times, and End BG. The BG Difference and Calculated Factor columns fill in automatically.
  • Confirmation Runs: Includes dedicated control rows for 24-hour follow-up confirmation tests.
  • Summary Dashboard: Automatically averages your test results by time of day and provides rounded recommendations for daily use.
• Tab 3 – “Correction Calculator” (Daily Use):
  • Section 1: Enter your Total Daily Dose (TDD) to get theoretical target estimates using the 1800 and 100 rules.
  • Section 2: Enter your current BG, target BG, and factor to calculate both exact and rounded practical doses in IU.

Important Considerations

• Use Time-of-Day Factors: Apply your morning factor for morning corrections and your evening factor for evening corrections.
• Safety Interval: Always allow at least 3 to 4 hours between corrections to prevent dangerous insulin stacking.
• Consultation: Always review test results and dose adjustments with your healthcare/diabetes team.

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