There are many ways to dose mealtime insulin. One way, called matching insulin to carbohydrate or advanced carb counting, involves the use of two ratios. One ratio tells you how much insulin you need for a given amount of carbohydrate and the other ratio tells you how many points one unit of insulin will drop your blood glucose.
You might have been given the ratios by your health care professional, or maybe you calculated your ratio from an equation, or you could have completed a series of food and blood glucose records and had the ratios calculated from the information in these notes. If your ratios were calculated a long time ago, how do you know that they are still adequate and, even more importantly, how do you change them if they are not?
There is a simple way to determine if your ratios are doing their jobs. In addition to the two ratios, you were most likely also given a blood glucose target or goal to aim for—somewhere between 100mg/dl and 150mg/dl. The lower end of the range is often used for young, healthy adults and pregnant women who want tight control of their blood glucose, while the higher range may be used for those who are at risk for frequent episodes of hypoglycemia.
If your ratios are on target, your blood glucose three hours after injecting insulin should be within a 40 point range from your goal number. For example, let’s say you are using a correction factor of 50. This would mean that each unit of insulin would drop your blood glucose 50 points. If your target blood glucose was 100 mg/dl, then, if your ratios are accurate, your glucose level three hours after a correction dose should be between 60 mg/dl and 140mg/dl. But keep in mind that 60mg/dl is a low reading and if your glucose level is often in this range after you take a correction dose, it is likely that your correction factor is too strong.
When you check your correction factor you should make sure your blood glucose is above 180mg/dl, that you are not having anything to eat or drink and that you were not recently physically active. If you are also evaluating your carbohydrate ratio you want to make sure your blood glucose is in target range before you eat so you don’t have to give a correction, that you know the specific grams of carbohydrate in the meal and that your meal is low in fat and doesn’t contain alcohol.
If, when testing your correction factor you land outside of your target zone on two or more occasions, a modification of your correction factor would be in order. To do this you would subtract your current blood glucose level from your starting blood glucose level and then divide the number of insulin units taken into the result.
Here’s an example: Starting blood glucose = 300, ending blood glucose = 200. The correction reduced your glucose level by 100 points. If you took 5 units of insulin, your correction factor would be 20 (300-200=100/5 =20), if you took 10 units it would be 10.
Knowing how your correction factor works and being able to adjust it when life changes can keep you ahead of the curve in your diabetes management.