The insulin-to-carbohydrate (I:C) ratio represents how many grams of carbohydrate are covered by one unit of insulin. You can estimate your I:C ratio using a formula that involves your total daily dose (TDD) of insulin.
Calculating Insulin-to-Carbohydrate (I:C) Ratio
The most common method to estimate your insulin-to-carbohydrate ratio (I:C) uses the "500 Rule." This rule provides a starting point for determining how many grams of carbohydrates are covered by one unit of rapid-acting insulin.
Here's how to calculate it, according to the "500 rule":
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Determine your Total Daily Dose (TDD) of Insulin: This is the total amount of insulin you use in a day, including both your long-acting (basal) and rapid-acting (bolus) insulin.
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Apply the Formula: Divide 500 by your TDD. The result is your estimated I:C ratio.
- Formula: I:C Ratio = 500 / TDD
Example
Let's say your total daily dose of insulin (TDD) is 50 units.
- I:C Ratio = 500 / 50 = 10
This means that one unit of rapid-acting insulin will cover approximately 10 grams of carbohydrates.
Important Considerations
- Individual Variation: This is an estimate. Individual insulin needs vary significantly. Factors such as activity level, stress, illness, and time of day can impact your I:C ratio.
- Work with a Healthcare Professional: It is crucial to work closely with your doctor or a certified diabetes educator (CDE) to determine your optimal I:C ratio. They can help you fine-tune the ratio based on your blood glucose readings and lifestyle.
- Monitoring and Adjustment: Regularly monitor your blood glucose levels, especially before and after meals, to assess the effectiveness of your I:C ratio. Keep a log of your food intake, insulin doses, and blood glucose levels to identify patterns.
- Correction Factor: A related calculation is the correction factor (or insulin sensitivity factor), which estimates how much one unit of insulin will lower your blood glucose. This is often calculated using the "1800 rule" (1800/TDD).
By using the 500 rule as a starting point and working with your healthcare team to fine-tune your I:C ratio, you can improve your blood glucose control and manage your diabetes more effectively.
