Question from Lakewood, Colorado, USA:

My son (age 13, 120 pounds, duration 3 years, athletic) takes 29 units of Lantus and anywhere from 20 to 35 units of NovoLog a day. The dose of NovoLog is dependent on the fasting blood sugar measurement before the meal, amount of carbs in meal, time of day (breakfast, lunch, dinner, and bedtime), day of week (weekday vs. weekend), and extra activity level (such as a basketball practice before or after meal). His total daily dose and weight indicate that he is probably completely dependent on outside insulin.

I am somewhat confused as to why his insulin sensitivity (number of mg/dl dropped by 1 unit of insulin) seems so different than the 1500 or even the 1800 rule so often quoted even after we scale for time of day, day of week, and extra activity level. I use anywhere from 50 to 68 mg/dl per unit insulin depending on the time of day. Using the rules and assuming an average total daily dose of 55 units the calculated insulin sensitivity would range from 27 to 32 mg/dl per unit insulin.

Instead of using these rules, I have taken a different approach with some success. Rather than base my calculations on the action of 1 unit of insulin, I now base my calculations on the action of 15 grams of carbs. For example, I now know that it takes 1.5, 1.1, and 1.5 units of insulin to cover 15 grams of carbs for breakfast, lunch, and dinner. I also know that 15 g of quick acting glucose tabs raises the blood sugar about 75 mg/dl at any of these times, provided there has not been significant exercise which causes the blood glucose to be used to replenish liver and muscle stores rather than raise blood sugar. Consequently I use 1.5, 1.1, and 1.5 units of insulin to reduce 75 mg/dl of blood sugar in excess of 150 mg/dl at breakfast, lunch, and dinner.

I should add that we rarely do a correction alone. Corrections are almost always done at meal time. Since it seems to work for me, I am wondering why other people do not do it this way too. Is there something wrong with this approach?