Carbohydrate Counting and Insulin dose adjustment

Insulin dose adjustment

The insulin dose adjustment is the next step in learning carbohydrate counting.

In the first 2 steps of carbohydrate counting, explained in the previous leaflet, you would have learned to identify the carbohydrate rich foods and estimate the amount of carbohydrate in these foods using food labels and Carbohydrate Reference Tables.

Once you know how to estimate the carbs in your meals, it is now time to learn how to adjust your insulin dose according to the amount of carbs at your meal, which is Step 3 of carbohydrate counting.

Step 3: Calculate the insulin dose
The appropriate insulin dose at your meal is worked out using the carbohydrate content of your meal in grams divided by your personal insulin to carbohydrate ratio (ICR).

The ICR specifies the number of grams of carbohydrate that is covered by each unit of rapid acting insulin. The ICR is different for everyone and may vary depending on the time of day. These ratios also may change over time when you are growing and going through puberty.

For example:
Your ICR may be: 1 unit of rapid insulin to 10 grams of carbs (ICR 1:10) or
1 unit of rapid insulin for 15 grams of carbs (ICR 1:15) or
1 unit of rapid insulin for 8 grams of carbs (ICR 1:8)

Your diabetes team will work out your ICR for you.

Once you are given your ICR, you will use it to calculate how much insulin you need at a meal depending on the amount of carbohydrate in that meal.

Basically you divide the amount of carbs in grams by the ICR.

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For example: if you having 60g of carbs and your ICR is 1:10, you divide 60 by 10 which gives you an insulin dose of 6 units.

Use your insulin to carbohydrate ratio to work out how much insulin you need to take to cover the carbohydrate in your meals or snacks.

INSULIN CALCULATOR

You may want to use the insulin calculator to find (without using an actual calculator) the dose of insulin you need for different amount of carbs using your ICR.

On the top bar of the table across you find your IRC for that meal and on the bar on the left hand side find the amount of carbs. To find your insulin dose slide your finger down the column which has your OCR on the top until the row which has the amount of carbs. For example: if your ICR is 1:15 and you have 100g of carbs, the insulin dose is 6.5 units.

Now have a go at working out your insulin dose for different meals based on your ICR and the amount of carbs in your meal. Either use the ‘insulin calculator’ on the previous page or use your calculator to divide the amount of carbs in your meal by your ratio to find the insulin dose.

How to work out the correction dose:
The ‘correction’ is used when your blood glucose level is high to work out the amount of insulin needed to bring your blood glucose to a normal level.

You will use the ‘insulin sensitivity factor’, also called the ‘correction factor’, which is an estimation of how much 1 unit of rapid acting insulin will lower your blood glucose level.

This correction factor is specific for each person as it usually depends on the average daily dose of insulin that the person needs.

Your diabetes team will calculate your ‘correction factor’ and to you how to use it.

Write your correction factor below:
1 unit of rapid insulin lowers blood glucose by ____ mmol/L

When you know your insulin sensitivity factor, you can work out your ‘correction bolus’, which is the insulin dose you need to lower your blood glucose to a normal level:

Current blood glucose – target blood glucose ÷ correction factor = correction bolus

Your target range will normally be 8 mmol/L.

Example:
Calculate correction bolus if your blood glucose is 16 mmol/l, target blood glucose 8 mmol/L and correction factor is 1:2 mmol/l.

16 mmol/L – 8 mmol/L ÷ 2 = 4 units

Now practice working out the correction bolus:
Pre-meal blood glucose: 18 mmol/L
Target blood glucose: 8 mmol/L
Insulin sensitivity factor: 1 : 5 mmol/L

Current blood glucose – target blood glucose ÷ correction factor = correction bolus

Guidelines and caution for using correction boluses:

• Check blood glucose 2-3 hours after giving correction bolus
• Do NOT give correction bolus less than your target range
• Do NOT correct if it has been less than 2 hours since your last correction bolus
• If a correction bolus is given between meals, the dose may need to be lower
• Do NOT correct a high blood glucose if you had a hypo in the last 4-6 hours
• If your blood glucose meter has the correction dose programmed in, check your settings!

Calculate total insulin dose, including insulin for the meal and the correction dose
To calculate the total mealtime insulin dose you need to work out the amount of insulin
you need for the carbohydrate using your insulin to carbohydrate ratio and if your blood
glucose levels are high then you need to add the correction bolus (correction dose).

Insulin dose for the carbohydrate in the meal + Correction bolus = Insulin dose

Example:

Work out the insulin bolus for this meal:
Insulin to carbohydrate ratio: 1 unit to 10g CHO
Total amount of carbs in the meal: 30g
CHO bolus: 30g ÷ 10g = 3 units of rapid insulin

Then work out the correction dose:
Pre-meal blood glucose: 14mmolL.
Target blood glucose level: 8mmolL
Insulin sensitivity factor: 1u : 2mmol/L
Correction bolus: (14 – 8) ÷ 2 = 3 units of rapid acting insulin

Now add the insulin bolus for the meal and the ‘correction dose’:
3 units (for food) + 3 units (correction bolus) = 6 units (total insulin dose)

Step 4: Physical activity:

• You may need a snack of 15 to 30 g carbohydrate for every 30 to 60 minutes of exercise, depending on the exercise intensity.
  The duration and intensity of exercise will affect the amount of carbohydrate that you need.
• If the exercise is more than 30 minutes and it is quite intense, you may need to reduce the doses of your rapid acting insulin.
• If you are planning to be physically active soon after the meal, you can consider reducing your insulin dose at that meal, which will give you more energy for the exercise and you may not need a snack.
• You may need to reduce your rapid acting insulin dose at a meal after the physical activity to have enough glucose to replenish the muscle stores and prevent a hypo.
• Discuss this further with your Diabetes Team.

Step 5: Adjust insulin doses
When you have learned carbohydrate counting and you are able to adjust insulin doses according to your blood glucose levels, it is important to also learn to adjust the ICR to get accurate insulin doses and keep blood glucose levels in range.

In order to adjust insulin doses, you need to know which insulin has an effect on your blood glucose at what time. Have a look at this table:

Adjusting the ICR according to blood glucose levels:
Your diabetes team will help you with adjusting the ICR initially, but in long term it would be good for you to know how to do that by yourself, or at least to know when you need to highlight to your diabetes team that you think your ratios need to be altered.

• To test if your ICR is well adjusted you will need to choose a day when your blood glucose level is below 10 mmol/l, no hypos in the previous 12 hours and no strenuous physical activity on that day.
• For testing your ICR choose meals that are balanced if possible, meaning that the meal has a moderate amount of carbs, some vegetables and is not too high in fat.
• You need to carb count as accurately as you can and then calculate your insulin dose using your current ICR.
• Check your blood glucose before the meal. You can test your ratio when your blood glucose if anywhere between 4 to 10 mmol/l. Do not give a correction dose, just the insulin to cover the carbohydrate. If your blood glucose is above 10 mmol/l you would not be able to test you ICR at that meal, as you would need to give a correction, therefore the ICR test would not be accurate.
• You then need to test your blood glucose about 4 hours later, without having any carbs inbetween.
• If your blood glucose is within 2 mmol/l to what it was before the meal, it means your ICR is well adjusted.
• If there is more than 2 mmol/l difference between blood glucose before the meal and 4 hours later, it means that you probable need to adjust the ICR. To be sure that the ICR needs adjusting, it would be advisable to repeat the ICR test once or twice before making any changes.

Adjusting the insulin to carbohydrate ratios:
Over time the amount of carbohydrate you need for each unit of insulin may change.
You can adjust your ratios for each meal by looking at patterns in your blood glucose levels.

Use this scale to find out which way.

Your diabetes team will help you to calculate your insulin to carbohydrate ratio and will show you how to adjust it according to your blood glucose levels

If your symptoms or condition worsens, or if you are concerned about anything, please call your GP, 111, or 999.

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