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Adjusting Insulin-to-Carbohydrate Ratios

in an Insulin Pump Program

Advanced Insulin Adjustment

Background Reading for this Article...
If you have not done so already, we recommend that you read the following WaltzingTheDragon.ca pages on insulin adjustment for pumps as background for the information that follows:

A Basal-Bolus Approach to Insulin Pump Therapy

How Insulin Action Impacts Blood Glucose in an Insulin Pump Program

Insulin Adjustment for Pumps: an Overview

Pump Record Review

Testing and Tweaking Basal Rates in an Insulin Pump Program

What is an Insulin-to-Carbohydrate Ratio?

 
An Insulin:Carb (I:C) Ratio specifies how much insulin is given to cover the carbohydrate-containing foods your child eats. Or, in other words, the I:C ratio specifies how many grams of carbohydrates are covered by one unit of insulin. That is, you give 1 unit of rapid-acting insulin for every X amount of carbs your child eats.

For example, if your child’s I:C ratio is 1:10, that means that 1 unit of rapid-acting insulin is given for every 10 grams of carbs eaten; if the I:C ratio is 1:15, 1 unit of insulin is given for every 15 grams of carbs eaten.

As an extension of this example, if your child uses a 1:15 ratio at breakfast you will give 1 unit of rapid for 15 grams of carb, 2 for 30, 3 for 45, 4 for 60, and so on (as well as 1.5 units for 22grams of carbs, and so on for other fractions of a unit).

A Note About Initial I:C Ratio Settings

If your child is about to begin using an insulin pump, the I:C ratios that will initially be programmed into the pump should be provided by your child’s doctor and diabetes health care team, based on the pre-pump I:C ratios that worked for your child with injected insulin, and/or your child’s age, size, growth stage, and activity level. As your child grows, changes will need to be made to these programmed I:C ratios. Periodically, you may want to test/verify how well your child’s existing I:C ratios are meeting her current need for insulin to cover food. You could then use the results as a basis of discussion with your child’s diabetes health care provider.

Assessing Current I:C Ratios (Pump)

Some things to note about I:C ratios:

  • As basal rates are the foundation for all the other insulin dosing which is layered on top, it is wise to verify the current basal rates before proceeding with fine-tuning of I:C ratios.
  • As noted previously, bolus insulin needs vary from person to person, and may be different at different times of the day. Therefore it is important that you check/fine-tune I:C ratios separately for each meal and snack.

 

Conditions for Assessing Current I:C Ratios

In order to eliminate confounding variables and obtain valid results from the I:C Ratio testing process, it is preferable for your child to get as close as possible to the following circumstances:

  • Eat a healthy meal/snack for the test, avoiding fatty foods and restaurant/takeout food. Ensure the carb-content of the meal is known.
  • Finish the meal within a reasonable amount of time (~1/2 hour) and then not eat/drink (except water and diet drinks) after the target meal or snack is finished.
  • Not exercise during the test period. (Light to moderate physical activity is okay, if your child consistently does so at that time of day.)
  • Not have had any lows in the 12 hours prior to the meal being tested.
  • Not be sick. (If you suspect that she is, postpone the test for another day.)
  • Not be at the beginning of or just prior to her menstrual cycle.
  • Not be experiencing significant stress or excitement.

In addition:

  • There should not be any other bolus insulin acting during the test period. This means that if a correction bolus for high blood glucose was given at the start of a meal, or within 4 hours prior to the meal, the data for that meal should be disregarded.

The I:C Ratio Test Process

  • For 1-2 weeks, for each meal which fits the conditions outlined above, take a blood glucose reading before the meal and 3 hours after the meal is finished.
  • Looking only at those meals which fit the conditions above, compare your child’s pre-meal blood glucose to that at 3-hours post-meal.

Adjusting I:C Ratios Based on the Test Results

If the results show that blood glucose is often above or below the target range following a particular meal or snack, consider changing the I:C ratio by 1-2 points (or more for teens and young adults, who are typically bigger and less insulin sensitive). To illustrate:

  • If blood glucose was about the same from the pre-meal to the 3-hour-post-meal check, no changes to the I:C Ratio seem to be needed at this time.

For example, if the current I:C ratio is 1:10, and if the blood glucose reading was 8.9 before the meal and 9.2 after the meal, this verifies the current I:C Ratio – it may be left at 1:10.

  • If blood glucose dropped by 2.0 mmol/L or more from the pre-meal to the 3-hour-post-meal check, consider a decrease in the insulin delivered for that meal by increasing the “C” (second number) in the I:C ratio.

For example, if the current I:C ratio is 1:10, and the blood glucose reading was 8.9 before the meal and 5.6 after the meal, you could choose to try an I:C ratio of 1:12. It is a good idea then to repeat the test and make additional adjustments which you feel are appropriate.

  • If blood glucose rose from the pre-meal to the 3-hour-post-meal check, consider an increase in the insulin delivered for that meal by decreasing the “C” (second number) in the I:C ratio.

For example, if the current I:C ratio is 1:10, and the blood glucose reading was 8.9 before the meal and 13.3 after the meal, you could choose to try an I:C ratio of 1:8. Again, it is a good idea then to repeat the test and make additional adjustments which you feel are appropriate.

If you do not see patterns in your child’s post-meal blood sugars, or are unsure of what to do, consult your child’s diabetes health care team for guidance on how to adjust the I:C ratios.

Next Steps for Adjusting Insulin within an Insulin Pump program:
Assessing and Adjusting Pump ISF Settings

The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.

This material has been developed from sources that we believe are accurate, however, as the field of medicine (in particular as it applies to diabetes) is rapidly evolving, the information should not be relied upon, as it is designed for informational purposes only. It should not be used in place of medical advice, instruction and/or treatment. If you have specific questions, please consult your doctor or appropriate health care professional.

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