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How to test your insulin carbohydrate ratio

If you are on multiple insulin injections or the insulin pump you will need to calculate how much insulin you have to give with your meal for every 10g of carbohydrate you eat.  This can vary from 0.5 units of insulin per 10g of carbohydrate to as much as 2.5 units per 10g of carbohydrate in teenage boys. When you start on multiple insulin injections or the pump, you should be given a ratio by the Diabetes Team but this will change as you grow and needs to be reviewed every few months. 

Below are the instructions on how to test insulin carbohydrate ratio

1. Test your blood glucose before a meal
2. Eat the test meal (see below for examples) with the amount of insulin you normally use
3. If you are high before the meal, do not use a correction dose for the purposes of this experiment
4. After 2 hours, test your blood glucose again if you are using the correct ratio your blood glucose should be within 2-3mmol of the before meal level.  If your blood glucose is higher, you need more insulin per 10g carbohydrate
5. After 4 hours, check your blood glucose again and it should be the same as the before meal level.

Examples of test meals

Test meals need to have an easy calculated amount of carbohydrate, that works quite quickly e.g.

Test meal 1

• 2 weetabix and 200ml (1/3 pint) of milk = 20g + 10g = 30g carbohydrate

Test meal 2

• 2 medium slices of toast and 100ml of fresh orange juice = 30g + 10g = 40g carbohydrate

Test meal 3

• sandwich as 2 slices medium bread or packet sandwich with label + muller light yogurt = 30g + 17g carbohydrate

Test meal 4

• medium jacket potato with cheese = 50g carbohydrate

Calculate the insulin

* You must round up or down to the nearest 10g

(If you are unable to give 1/2 units of insulin, either wind up or wind down the dose of insulin)

Example of a test meal

• Blood glucose before eating 9mmol/L
• Normal ratio is 1 unit per 10g of carbohydrate
• A meal is 30g therefore 3 units of insulin given before meal
• Blood glucose 2 hours after eating 15mmol/L
• Blood glucose 4 hours after eating 13mmol/L

Conclusion

1 unit per 10g is not enough insulin.  Try increasing it up to 1.5 units per 10g and repeat test meal.

It is important to note that sometimes the ratio varies dependent on the meal, quite often breakfast needs a higher ratio than other meals and the fine tuning can only be done by checking blood glucose before and after individual meals.  For more information on bolus insulin and insulin pumps.