BOLUS Insulin  calculation.

Deciding Bolus quantity - First step for deciding bolus is to calculate carb content of meal. Once Carb in grams is calculated, there are several methods to determine Insulin dose. For the beginner, easiest to follow is Carb Factor, calculated by Rule of 500.

CARB FACTOR = 500 / TDD (total daily dose of Insulin)

For example, if TDD is 50 units then Carb factor would be 500 / 50 = 10.

This means, for 10 grams of carbs 1 unit of Insulin bolus is needed.

Another formula to reach Carb factor is to multiply Insulin Sensitivity Factor or Correction Factor by 0.33. For example, if Correction factor is 45 then Carb Factor will be 45 multiplied by 0.33 that is 15.

Carb factor depends on patients Insulin sensitivity. Generally, the more Insulin sensitive, the higher will be Carb factor. For example a patient with Carb factor of 25 is more Insulin sensitive then a person with a Carb factor of 15 . In addition, patients may be more or less insulin sensitive at different times of day and they may have a different Carb factor at breakfast and dinner.

Since Insulin sensitivity also changes during many situations so Carb factor may also need to be revised if -

            • Total daily dose of insulin changes

            • Body weight changes more than a few kilos

            • During infections, illness or pregnancy.

After few days of pump use, a more precise method can be used to make Carb factor calculation more accurate. Pump user need to record information about food intake, insulin dose, and SMBG.

Patient needs to keep 3-7 days of records, including:

            1.         Premeal, and 2-h PPG results

            2.         Premeal insulin doses

            3.         Amount of Carbohydrate consumed.

Example;

            •           Consumed 60 gm carbohydrate

            •           Used 5 units rapid acting insulin

            •           PPG was with in 30 mg of  pre meal value 

            •           60 / 5 = 12

            •           Carb factor reconfirmed to be  12

Thus, the  practical way is to check  blood Glucose before eating a meal, then eat a meal, whose Carb is correctly known ,then bolus the calculated Insulin quantity. Now, recheck Glucose again after 3 hours. If, the pre meal Glucose level and after 3 hours Glucose is ± 30 mg then Carb factor is correct. While if post meal value became high then Carb factor needs to be increased and vice versa.