If I Eat More Carbs, When Should I Bolus?
I use a meter programmed to my insulin pump. After I test for blood glucose and bolus for what I intend to eat, if I am still hungry and want to eat more 10 to 15 minutes later, can I just bolus for the extra carbs? Name Withheld
Alison B. Evert, MS, RD, CDE, responds:
Yes, if you eat more carbohydrate, you should deliver an additional insulin bolus for this food. Eating more carbs will increase your blood glucose level. Some health care providers may recommend not taking additional bolus insulin unless you eat more than 15 grams of carbohydrate. Check with your health care provider for your individual instructions.
However, you should not take more correction insulin when you deliver the additional food bolus. This is called "stacking insulin," and it can put you at risk for a low blood glucose reaction. To understand the idea of stacking insulin, you have to consider your "insulin on board," the amount of insulin that is active in your body. Your premeal dose, or bolus, includes mealtime and often correction insulin if your blood glucose level is above your target before eating. As soon as you deliver a premeal dose, your pump tracks the insulin on board for you.
Most pumps use rapid-acting, or mealtime, insulin (aspart, lispro, or glulisine). Whether it's delivered by pump or injection, it works the same. Rapid-acting insulin's onset of action is about 10 to 15 minutes. Its effect peaks in about one to two hours, and its duration is about three to four hours. (For more on using mealtime insulin, see "Insulin's Ins and Outs".)
Many pumps have a bolus calculator feature. Your health care provider sets the calculator based on your needs. The settings include your blood glucose target range, an insulin-to-carbohydrate ratio for mealtime insulin, an insulin correction or sensitivity factor to bring your blood glucose back into target range, and your active insulin time (often set between three and six hours).
If you use the bolus calculator feature, it will take all these factors into account. It will tell you how much insulin is needed to cover a certain amount of carbs and correct your blood glucose level if needed. Let's say you took a mealtime bolus of 10 units of insulin (8 units for carbs and 2 units for correction). One hour after the bolus, about 8 units of insulin are still working in your body. So, if you took more correction insulin after the premeal bolus, you would be stacking: layering additional correction insulin on your previous dose. Most health care providers recommend waiting three or more hours before delivering another correction bolus.