A ratio that specifies the number of grams of carbohydrate covered by each unit of rapid- or short-acting insulin. This ratio serves as the foundation for adjusting premeal bolus insulin doses.
Counting grams of carbohydrate (or carbohydrate “choices”) and using an insulin-to-carbohydrate ratio allows a person to give himself just enough insulin to cover the carbohydrate he plans to eat. This means he doesn’t have to eat the exact same amount of carbohydrate for a given meal each day. Knowing how to count carbohydrate and use an insulin-to-carbohydrate ratio is valuable for tightly managing blood glucose levels, and it is essential for using an insulin pump effectively.
A fairly typical insulin-to-carbohydrate ratio is 1 unit of insulin for every 15 grams of carbohydrate. However, the ratio varies considerably from one person to another, and a person’s own ratio may change over time or even from meal to meal. For instance, a person may need 1 unit of insulin for every 10 grams of carbohydrate at breakfast but 1 unit for every 15 grams of carbohydrate in the evening. This can be due to factors such as how much insulin is already in a person’s system, how much physical activity he has done, and fluctuations in his hormone levels throughout the course of the day.
Your health-care team can help you determine your own insulin-to-carbohydrate ratios based on your blood glucose and meal records. Be sure to note the number of grams of carbohydrate in the meal, your blood glucose level before the meal, the number of units of insulin in the premeal bolus, and your blood glucose level 3–4 hours after the meal. It’s a good idea to gather 10–14 days of data before settling on a ratio.