Introduction: Diabetics: How to Calculate High Blood Glucose Correction Using the Rule of 1800

The mantra of a diabetic is control.

Having blood sugars out of control leads to all sorts of bad things. Like (for the guys) impotence. You want normal blood glucose  levels. As a diabetic, this is one of the health choices you want to make.  Trust me on this one.

Some Diabetes 101:
You need insulin for cells to use sugars. Type 1 Diabetics do not produce insulin, and need to take insulin shots or injections. Food makes blood sugar go up. Insulin makes it go down. Too much sugar for too long damages the body. Too little blood sugar makes you pass out. The job of a Type 1 diabetic is to walk  a tightrope and keep the blood sugar in a certain range. Diabetics use a glucometer to test their blood sugar.

(NOTE: This is a dramatic oversimplification. Stress raises blood sugar levels. Exercise will help drop it. But you get the picture). 

Step 1: Time to Play With Math!

Blood glucose is the amount of sugar in your blood.  The normal range for blood glucose on a fast is 80 to 110 milligrams per deciliter. As a diabetic, I fudge a little on that range...I might fall below 80 or run up a little higher. But the goal is to keep the blood glucose in a fairly tight range.

One important lesson for the diabetic is how to calculate an insulin correction factor. The insulin correction factor (or insulin sensitivity factor) is a bolus of insulin to bring down a higher than range blood sugar level. In order to know this factor, you need to know how much one unit of rapid-acting insulin will drop the blood sugar! Time to play with math!

Step 2: The Rule of 1800

There are several simple formulas for figuring this out.

In general, one unit of rapid-acting insulin will take care of about 12-15 grams of carbohydrate, but this can range depending on a lot of factors. Besides, it is useful to do the math and know what you need!

(I have met many diabetics who never heard of the following formula. Knowing how to calculate a correction dose is invaluable to good blood sugar control, and will greatly help anyone diagnosed with Type 1 Diabetes) 

The Rule of 1800!

Correction Factor = 1800 ÷Total Daily Insulin Dose (TDD) = 1 unit of insulin will reduce the blood sugar so many mg/dl

My TDD for yesterday was 85.4 units. (The TDD is the total amount of insulin I take in a day. My basil or background rate is 48.8 units. I use an insulin pump that is  constantly feeding me a small amount of insulin. I take boluses prior to meals and snacks, and those amounted to 36.6 units - adding to 85.4).

So... 1800 ÷ 85.4 = 21.

High blood sugar correction dose = Difference between actual blood sugar and target blood sugar ÷ correction factor.

For example, at lunch today I was 280! (it happens). I want to be around 140 for lunch.

280 - 140 = 140

140 ÷ 21 = 6.6 units of insulin.

So in addition to my normal bolus for lunch, I would take an addition 6.6 units to bring down that high blood sugar!

I recommend recalculating the correction periodically to keep tabs on how your body is changing.

Of course, these formulas all represent "initial best guesses” and you must modify your insulin schedule for on target blood sugars. I work with my endocrinologist, diabetes center, and my general doctor. Please do not take my word for anything. I am a big liar. All art from

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