grams/(1 unit/25 grams) = 1.6 units of insulin. The patient will need to inject 1.6 units of insulin to cover the anticipated meal. ● Finally, add both values together: 0.5 unit + 1.6 units = 2.1 units. Depending on the patient’s method of insulin injection, the calculated value may need to be rounded to the nearest measurable increment. This should be discussed as part of the training and education upon diagnosis. Healthcare Consideration: An insulin-to-carbohydrate ratio (ICR) is utilized to calculate insulin requirements to cover carbohydrate ingestion. While an initial single value may be calculated, some children require different ICRs throughout the day. In many patients, the ICR is lower for lunch than for breakfast or dinner. This is especially observed in children, as their ICR varies in response to their level of activity throughout the day (Tascini et al., 2018). Creating the above example requires two pieces of information: Calculation of the patient’s ISF/ICR and the ability to read a food label. The patient’s initial ISF and ICR is calculated based on the estimated total daily dose of insulin and the insulin type utilized for prandial doses. For patients receiving rapid-acting insulin, the “rule of 1800” is used to calculate ISF, and the “rule of 500” is used to calculate ICR (Tascini et al., 2018). Other “rules” can be applied for patients on short-acting insulin. This course will focus on the more commonly used rapid-acting insulin products. In the above example, the patient weighs 40 kg. The total daily dose of insulin is calculated using the lower end of the weight-based calculation: 0.5 unit/kg = 20 units. Half of that value is given as a basal dose, and the other half is anticipated to be prandial. The “rule of 1800” dictates taking 1800 and dividing that value by the calculated total daily dose of insulin. In this case, 1800/20 = 90. This patient’s ISF is therefore 1:90. Similarly, the “rule of 500” dictates taking 500 and dividing that value by the calculated total daily dose of insulin. In this case, 500/20 = 25, resulting in an ICR of 1:25. These “rules” are useful in determining initial estimates for a patient. Over time, the values can be adjusted based on blood glucose trends and goals for glycemic control. Self-Assessment Quiz Question #4 Rob weighs 30 kg, and his estimated total daily dose of insulin is 16 units (~0.5 unit/kg/day). What would you recommend for Rob’s insulin sensitivity factor (ISF) and insulin-to-carbohydrate ratio (ICR) if he is prescribed insulin lispro?
Evidence-based practice! While a majority of insulin dosing regimens are based on carbohydrate counting, other macronutrients’ impact on glucose control are undergoing study. A new concept called a food insulin index takes protein and lipids into consideration for insulin dose calculations. A small study evaluated this algorithm in adolescents with type 1 diabetes mellitus and found that this method led to less postprandial glucose excursions compared with carbohydrate counting (Erdal et al., 2021). The food insulin index algorithm may achieve improved glycemic control after consumption of high glycemic-index meals, but these findings must be confirmed in larger trials before becoming standard of care. Some food items may not be measurable in distinct servings. In those cases, portions must be weighed prior to consumption to determine the serving size and concomitant carbohydrate count. Household food scales are required for measuring meals, especially in young patients with small portion sizes and less margin for error. Occasionally, it may not be possible to precisely calculate carbohydrate portions. This may occur when out to eat, either at a restaurant or a party. In these cases, there are tools for estimating portion sizes, one of which recommends measuring with a hand, particularly a woman’s hand size. Utilizing this method, a fist is equivalent to approximately 1 cup or 30 grams of carbohydrates for foods such as a cooked cereal or ice cream. A thumb is about 1 tablespoon, and a thumb tip is approximately 1 teaspoon. It is recommended to practice these measurements, compared to known portion sizes, in order to determine level of accuracy. Self-Assessment Quiz Question #5 Rob and his mother are adjusting to the new diagnosis and participating in education. It is time for Rob’s lunch, and you are going to observe his mother’s insulin calculations. He plans to eat one container of yogurt (serving size: one container, carbohydrates per serving: 33 grams), 1 slice of whole grain bread (serving size: 2 slices, carbohydrates per serving: 34 grams), 1.5 tablespoons of hazelnut spread (serving size: 2 tablespoons, carbohydrates per serving: 22 grams), and 1/3 of a banana (serving size: 1 banana, carbohydrates per serving: 27 grams). His preprandial blood glucose level is 155 mg/dL, and his goal blood glucose is 100 mg/dL. Given his ISF and ICR (calculated in question 4), how many units of insulin should she inject prior to his lunch?
a. 1.5 units. b. 2.5 units. c. 3 units. d. 4.5 units.
a. ISF: 60; ICR: 1:16 b. ISF: 16; ICR: 1:60 c. ISF: 30; ICR: 1:110 d. ISF: 110; ICR: 1:30
For completeness, there are other methods of multiple daily insulin injections with less flexibility (ADA et al., 2022d). Rather than a calculated ISF/ICR, patients are scheduled to receive a set distribution of insulin throughout the daily. These regimens use different combinations of short-acting insulin, rapid-acting analogs, and/or NPH insulin to provide basal and prandial coverage. The most simplified regimen only requires twice-daily injection consisting of mixed NPH insulin with regular insulin or a rapid acting analog. By combining different types of insulin with varied pharmacokinetic properties, acceptable glycemic control can be achieved; however, it is typically difficult to meet strict targets with these methods. There is also a greater risk of hypoglycemia, and patients must be relatively consistent with their carbohydrate intake on a daily basis. While these regimens are not preferred, they are an option for individuals unable to perform carbohydrate counting and/or inject multiple times throughout the day. These methods of administration are typically not preferred in the pediatric population because their eating habits are not consistent, insulin requirements change with growth and development, and tight glycemic control is best for prevention of lifelong complications.
Next, the patient must be able to accurately read a food label in order to determine the grams of carbohydrates in the meal. This skill, referred to as “carbohydrate counting,” is essential for insulin calculations and diabetes management. The most pertinent item on the food label for insulin calculations is grams of carbohydrates. Sometimes, the serving size will list a “gram” amount as the weight of the total product. This should not be confused with the amount of carbohydrates in each serving. The patient will also need to determine how many “serving sizes” they will be ingesting and adjust the reported grams of carbohydrates accordingly. For instance, if a child is going to eat bagel bites, which contain about 27 grams of carbohydrates per serving, the caregiver will need to check the serving size. In this case, the serving size is four pieces. If the child eats six pieces, the grams of carbohydrates will need to be multiplied by 1.5 (27 grams * 1.5 = 40.5 grams) to determine total carbohydrates ingested.
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