A. Let's assume your insulin to carb ratio is, for example, 1 unit of insulin for every 10 grams of carbs.
This is the number which is programmed into your pump to determine boluses for meals.
B. Let's also assume that your sensitivity in 30 mg/Dl for every unit of insulin. That is, 1 unit of insulin will
drop your blood sugar 30 points (mg/dL). This is the number which is programmed into your pump
for correction boluses.
IF 1 unit of insulin equals BOTH A. 10 grams of carbs AND B. 30 blood sugar points (mg/dL) THEN
A. 10 grams of carbs equals B. 30 blood sugar points (mg/dL) which simplifies as follows:
1 gram carbs = 3 sugar points (mg/dL)
In theory at least, what this implies is that for every one gram of carbs you eat without bolusing or, morelikely, to correct a low, your sugar should go up 3 points. You can use this information in the following way:
EXAMPLE: Say you just woke up with a 52 blood sugar and you want to ingest the exact amount of carbs to raise your blood sugar to 100. To figure it you would divide the difference between the two, 48, by 3, which is the number of sugar points you should get out of 1 carb ingested and get exactly 16
grams of carbs. Since most glucose tablets contain 4 grams of carbs, you would need to take exactly
4 glucose tablets. It also means that every single glucose tablet would raise YOUR glucose by 12 points.
You might ask, what if I do the calculations, try it and it doesn't work out that way. What does it mean?
It probably means that either you carb ratio or insulin sensitivity settings or both are incorrect. Now this is interesting because it gives you a very easy way to recalculate all three numbers. You would have to start with at least five hours of fasting, no exercise and a blood sugar of around 150. First, take 1 unit of insulin, wait a couple of hours, and see how far your sugar drops. This will give you your sensitivity. Now eat 2 or 3 standard glucose tablets, wait an hour more, and see how far your sugar rises.
To find your carb ratio, first divide the number of points your sugar rose after eating the tablets by the total number of carb grams in the tablets. Then divide your insulin sensitivity, which is the number of points your sugar DROPPED after taking the insulin, by the first number to get your carb ratio.
EXAMPLE: You tested your blood sugar, after fasting and no exercise, and it was 150. A couple of hours after taking exactly 1 unit of insulin your sugar dropped to 112. This tells you your sensitivity is the difference between 150 and 112, or 38. Next, an hour after eating exactly 2 glucose tablets (8 grams of carbs) your sugar rose from 112 to 144. So you divide the difference between 144 and 112, which is 32, by the 8 grams of carbs to get 4, Next you divide your sensitivity, 38, by 4 and get 9.5, which is your carb ratio. You should need 1 unit of insulin for every 9.5 grams of carbs you eat.