Adjust insulin in T1DM based on diet

Divide NO. of grams of carbohydrate eaten at meal by the NO. of units of premeal insulin (e.g., 45 g CA divided by 3 units of insulin is a 1:15 ratio)
Mahitab Hany, BS Pharm, PGDipClinPharm, PGDipClinNutrition

As a nutrition support pharmacist, you should know how to adjust insulin doses in patients with type 1 diabetes mellitus based on diet and weight. Advise the patient to record time of meals and snacks, the amount and type of food eaten, amount of carbohydrate consumed, insulin dose, physical activity, and blood glucose results. Patients should first practice eating consistent amounts of carbohydrate at meals and snacks so that baseline insulin requirements can be matched to usual carbohydrate intake using pre- and postprandial blood glucose testing results. When pre- and postprandial blood glucose levels are in the target range, then insulin-to-carbohydrate ratios can be determined as follows...

          Divide the number of grams of carbohydrate eaten at the meal by the number of units of premeal insulin (e.g., 45 g carbohydrate divided by 3 units of insulin is a 1:15 ratio). Insulin-to-carbohydrate ratios can vary with time of day and are affected by stress, illness, and variations in physical activity.

Two other methods to calculate insulin-to-carbohydrate ratios (see Table 1) are the 450 to 500 rule and the weight method. These methods do not take into account individual variation and, therefore, are not as accurate as using detailed records.

Table (1). Methods to calculate insulin-to-carbohydrate ratios
METHOD COMMENTS
450 to 500 rule Regular insulin-to-carbohydrate ratio = 450 divided by total daily dose (TDD) of insulin.
Rapid acting insulin-to-carbohydrate ratio = 500 divided by TDD of insulin.
As an example, if the TDD is 50 units and the patient uses a regimen with rapid-acting insulin, then each unit of insulin should cover approximately 10 g of carbohydrate (500 divided by 50 = 10). The insulin-to-carbohydrate ratio is 1:10.
Weight method The weight method uses the data below to calculate the insulin-to-carbohydrate ratio.
Weight (lbs) Ratio
120 to 129 1:15
130 to 139 1:14
140 to 149 1:13
150 to 169 1:12
170 to 179 1:11
180 to 189 1:10
190 to 199 1:9
> 200 1:8
To convert Kilograms to Pounds: 1 kilogram (kg) is = 2.2 pounds (lbs).

Elevated blood glucose levels — An insulin correction factor can be used to adjust insulin dose for hyperglycemia before or between meals. To calculate the insulin correction factor...
    • For regular insulin, divide 1500 by total daily dose (TDD) of insulin.
    • For rapid-acting insulin, divide 1800 by total daily dose (TDD) of insulin.

As an example, if a patient using rapid-acting insulin has a TDD of 45 units, then the insulin correction factor would be 1 unit for every 40 mg/dL reduction in blood glucose (1800 divided by 45). If the patient had a premeal blood glucose of 180 mg/dL and wanted to correct to a premeal blood glucose of 100 mg/dL, then the patient would take an extra 2 units of rapid-acting insulin to correct to the target of 100 mg/dL and add the number of units needed to cover the carbohydrates consumed.

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