Confused! Can someone help with figuring out the right correction factor?

Hey everyone!

I m trying to figure out my correction factor at the moment, and theres something I am confused about, so maybe you could shed some light on this for me:
So: When I eat a meal, I know that for instance with 12 g of carbs, it would raise my BG by about 40 -60 points. (This is if I do not inject any insulin).
If I bolus for it, I will need 1 unit for these 12 g to get me back down where I want to be. (More or less).
So is it then the correct conclusion to say "1 unit of Novorapid lowers my BG by about 40-60 points"?
And why can I not transfer that directly to what my correction factor is? So when I measure, I am about 140, I dont eat, but want to get back to my target of 100, I would inject 1 unit to correct, and land at around 100?
I am reading "Using insulin" at the moment, and the way they calculate the correction factor depends on the overall daily intake of insulin – they divide the daily units through 1800 – since I am still honeymooning my daily units average around 4 units, which would make my correction factor a 450 (!!) points drop per 1 unit of Novorapid?????

Obviously this cannot be right, I presume you cant apply the 1800 rule to someone on such a small TDD.
Am I having a big knot in my thought process here? I would be grateful for anyone who could "unknot me" ;))
Thank you!

This is from the book Using Insulin by John W.

Correction Factor
The 1800 Rule For Determining Your Correction Factor

When your blood sugar goes unexpectedly high, a correction bolus can be used to bring it down. To use the right correction bolus, you first determine your correction factor. The 1500 Rule for Regular was originally developed by Paul Davidson, M.D. in Atlanta, Georgia. Because the blood sugar tends to drop faster and farther on Humalog and Novolog insulin's, we modified the 1500 Rule to an 1800 Rule for these insulin's. (Some use a 2000 rule for these insulin's.) The 1800 Rule shows how far your blood sugar is likely to drop per unit of Humalog and Novolog insulin. The 1500 Rule shows how far it will drop per unit of Regular.

Numbers between 1600 and 2200 can be used to determine the correction factor. The number 1800 should work when the TDD is set correctly and the basal insulin makes up 50% of the TDD in someone with Type 1 diabetes. A number smaller than 1800 will work better when basal insulin doses make up less than 50% of the TDD, while a number higher than 1800 works better for those whose basal doses make up more than 50% of their TDD. Also recheck your TDD and basal percentage to make sure they are correctly set.

Setting up your correction boluses can be done only after your basal doses have been tested for accuracy. If your basal doses are set too high, using a correction bolus may lead to lows, while basal doses that are too low will make it appear that correction boluses are not the right amount to bring high readings down as expected.
The 1800 Rule:

Works for Type 1 diabetes and most Type 2s
Estimates the point drop in mg/dl per unit of Humalog or Novolog
1800/TDD = point drop per unit of Humalog (see Table)
Someone's Total Daily Dose of insulin = 30 units
1800/30 u/day = a 60 point drop per unit of Humalog
The 1800 Rule allows you to set up an accurate personal Sliding Scale to lower unwanted highs!

The formulas that Walsh uses in his book need to be adjusted if you are using a diet that is not 45-65% of calories from carbs.

An alternate rule of thumb is that an insulin sensitive person will rise 5-10 mg/dl for each gram of carb, thus you can guesstimate you correction factor as you the product of this number times you ICR. If you ICR is 20, then your correction factor is 100-200.

But frankly, if you only use 4 units/day, you can't really be properly bolusing for meals with sufficient precision and I would totally avoid correction. You just won't be able to get proper small doses anyway.

Great topic and one I had never thought about. I have been on my pump about 10 years and was told my correction was 1 to 65 and have always used that ratio. I did JohnG's calculation and I get 1/105. With the 1/65 ratio, it has always worked really well and seemed right on track, so I never worried about it.

Since I have been trying to avoid so many lows, my daily totals have decreased by about 25% and 1/65 still works great.

Hmmmmm. Very interesting. Will increase my awareness of the corrections.

The Using Insulin 1800 rule is for full T1, not for LADA with significant insulin production - so it really doesn't apply to you. Even for a T1, the 1800 rule is only useful to get an initial estimate for about what their correction factor should be. But then it is necessary to do your own testing to see what your personal numbers really are.

Your measurement of 40-60 for 1 unit is EXACTLY the right way to do it. So you have figured out your correction factor. Of course this is may change over time, but for the time being this is your number.

Also, I have found that my correction factor varies significantly depending on the time of day. From 50 points in the morning (most insulin sensitive) to 20 points at night (least insulin sensitive). You may see similar results - the only way to know is to do what you're doing, and test, test, test (fingers be damned!)