Insulin dose adjustment
The approach used to adjust insulin will be influenced by your insulin regimen (the type and amount of insulin taken).
Calculating bolus dose
To work out the bolus dose, you will need:
- Your personal Insulin-to-Carbohydrate Ratio (ICR).
- This is the amount of bolus insulin you need to inject at meals for a certain amount of carbohydrate.
- The ICR will vary from person to person and can be different for each meal.
- A starting ICR for most individuals is 1 unit of bolus insulin for every 10g of carbs (1 Carbohydrate Portion or CP). This is based upon the fact that 10g of carbs (1 CP) will increase blood glucose by 2 to 3 mmol/L, and 1 unit of bolus insulin will reduce blood glucose by the same amount.
- To work out the most suitable starting ICR for you, it is important to talk to a member of your diabetes care team.
- The total amount of carbohydrate consumed (grams / CPs). See the [Carb Counting] page for helpful tips on how to count carbs.
- When you know your ICR and have worked out the carbohydrate content of your meal, as the example below illustrates, you can calculate the amount of bolus insulin you need.
Example: Calculating the bolus dose
The following lunch contains 80g carbs (8 CPs).
With an ICR of 1 unit of insulin for every 10g carbs, you would need to inject 8 units of insulin for the lunch above.
Alternatively, if you are counting in carbohydrate portions (CPs) and have an ICR of 1 unit for every 1 CP, you would calculate the insulin dose in the following way, which has the same result of 8 units for the lunch above.
Insulin bolus dose adjustment and carb counting
When you feel confident in this approach you should be able to:
- Vary the times and the amount of carbohydrate you eat.
- Predict blood glucose response from different foods.
Twice daily mixed insulin regimen
Insulin used twice daily may contain a mixture of shorter and intermediate acting insulin (e.g. Humulin M3 and Novomix 30) and is taken twice a day at breakfast and evening meal. Individuals who are on this regimen are unable to adjust their insulin, but carb counting can be applied to maintain similar amounts at meals.
Multiple daily injection insulin regimen (basal bolus therapy)
Those who are on this regimen, are able to adjust their injection of bolus insulin (e.g. Humalog or Novorapid) at each meal time. The amount of bolus insulin taken is directly related to the amount of carbohydrate consumed.
As you must be able to accurately calculate the amount of carbohydrate you eat and drink before adjusting your bolus dose, a carbohydrate log can help you demonstrate this.
It can also be useful to record a detailed diary which outlines carbohydrate eaten, blood glucose, activity, bolus and basal insulin.
BERTIE is an online resource that provides additional information on the key principles of carb counting and insulin dose adjustment. It has been developed by the Bournemouth Diabetes Team.
Carbohydrate counting and insulin dose adjustment is a complex process. Before implementing this strategy, it is important to have the support and guidance of your diabetes care team.
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