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). 

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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 clipart.com

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    13 Discussions


    Reply 6 years ago on Step 2

    Thank you. I have been on a hiatus from instructables, but may have to author some new ones. I appreciate your comment. -r


    2 years ago

    Type 2 diabetics with insulin resistance will find this rule useless. Each patient must calculate her own ratio, bearing in mind that the ratio will change throughout the day. Type 2 is more complicated, but also manageable.


    3 years ago

    It's certainly misnamed - it's NOT a Rule - but a Rule of Thumb - a starting point which you adjust up or down. If you really want to tailor your correction ratio, use the PredictBGL App

    iTunes - http://itunes.apple.com/app/id980437930

    Google Play - https://play.google.com/store/apps/details?id=com.managebgl.predictbgl2


    3 years ago

    Great and helpful concept! Anyone know why this works?


    3 years ago

    Dear all,
    Here in The Netherlands we use the rule of 100, which happens to be equivalent to your rule of 1800. We work with mmol/l, you use mg/dL I guess. As your value is 18 times higher it should be the same.
    For those people, like me, who don't want to calculate Accu-Chek invented the Aviva Expert that calculates how much units to inject. You measure the blood sugar and the carbohydrates, this device show the amount of insulin to inject. It also gives a bolus advice if you don't want to measure.
    It remembers the time and amount of injected insulin in case you measure in between.

    In my case it is a very handy device as my ratio differs by the time of the day. In the afternoon I use less insulin and this machine can handle that too.

    aviva expert.jpg

    4 years ago on Introduction

    Thanks for the useful information! If i am using the SI unit of measure of mmol/L, the correction factor rule of thumb will be 100 / TDD i.e. 1 unit of insulin will correct 100/TDD mmol/L. The Rul of 100. (:

    I've been an insulin-resistant type 1 for 19 of my 23 years on this planet. Sadly, even with a formula, some days it'll work and some days it won't. Also not lucky enough to have a pump. One kidney currently not very happy but I'm working on it :\


    9 years ago on Step 2

    3 years T1 now...I use to follow a rule that roughly says that 1 unit of insulin makes the sugar in blood go down about 50mg/dl. So if I'm 250 and my goal is 100, the bolus must be 3 units. That´s useful if you don't use insulin pump, you can't inject 0,5 unit...

    1 reply

    Reply 9 years ago on Introduction

    Thanks for sharing. I recall the prepump days, and having those sort of correction guidelines are very useful! -r


    9 years ago on Step 2

    it looks like if you were a bad diabetic patient and you try to justify your meal sins...  Diabetes is a really hard disease and you will not try to make a game in it's control... This procedure can put your kidneys in troubles in short...

    2 replies

    Reply 9 years ago on Step 2

    Huh. I've been a Type 1 for 17 years and on the pump for 10 (The D-Tron and now the Accuchek Spirit). The Rule of 1800 is a well-recognized general way to start figuring out an individualized high blood sugar bolus. There are other methods, but this is a common one. High blood glucose levels happen, (whether from a miscalculation in carbs, or for the pump user the infusion site goes bad), and it is important to have a system in place. I would use the Rule of 1800 as a starting place.

    Uh...I am not sure how a method of correcting a high blood sugar would be bad. The goal is control.


    Reply 9 years ago on Introduction

    Type 1 for 49 years. (I'm 51.) Anyone not familiar with T1 doesn't realize that good control may not look like it from a "text book" (translation: what a non-diabetic's body does) standpoint and sometimes for some unfathomable reason, the sugar just spikes. I'm in good control (A1Cs under 7) and I have "those days" when nothing goes right. I've never seen the Rule of 1800 but I like it. I'm going to start playing with it (Hey, it's a deadly disease, might as well "enjoy" what we can, eh?) to see if it's easier than my method (which is "knowing because I've had it for 49 years & MUST know in order to keep on keeping on!) Thanks for posting this!!