Calculating Correction Doses

It means an average and should be a constant unless you've put on lots of weight or lost lots of weight.
Depending on the insulin taken the short acting stuff is out of the system after 4 hours so its important not to over correct.
My correction dose and I think I am average is 1 unit for 3 mmol. So if Ii were at 16 and wanted to get down to 7 I;d be putting in 3 units then testing.
Sadly this is more of an art than science but you have to start somewhere then workout what necessitated the correction dose in the first place...

I completely agree with @NicoleC1971 : correction doses are an art.
Unfortunately they vary too.
They may vary at different times of the day and they may vary at different BG readings and they vary per person.
The different times of the day part tends to follow similar patterns and times to your BG dose varying: unless you have a pump or a meter that calculates dose based on a timetable of insulin to carb ratios, most people will have an average correction rate. I think 1 unit for 3mmol/l is a common starting point for someone who has left their honeymoon period... at least it was mine.
The different BG readings is a little easier although it varies per person. Basically, as our BG rises, we are likely to become a bit insulin resistant so need more to correct. For example, for me, when my BG is over 15mmol/l, I need twice as much insulin to correct 1mmol/l.
Finally, the per person bit: the calculation you have quoted is guidance. It will depend on things like how many carbs you eat (compared to many on this forum, I eat a lot of carbs but my correction dose does not take this into consideration) and some indecipherable things which some higher being (like a research scientist) may understand but I certainly don't.

When trying to work out what works for you (or your friend), I would always underestimate, test, top up if necessary and keep your hypo treatment to hand.
I tend to correct every 2 hours when I am very high and use the rule of thumb that my body has used half the insulin I last injected. Like all of this calculation the "insulin on board" (IOB) is an approximation and, in this case, it is conservative.

mountaintom said:

So if my average bolus and basal for the day is 18 units I do : 100 / 18 = 5.5. And that therefore says that 1 unit of Novorapid will drop me 5.5 mmo/l?
Obvs this depends on lots of other things. But is this the idea?

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I am not aware of the formula so can't tell you but if you test before the meal (assuming this is more than 4 hours from your last dose then you will be clear of any bolus insulin by then).
Do the correction dose and check at 2 hours and 4 hours without eating anything so that your results are not confounded by a meal and another bolus.
You will be hungry but at least you will have a starting point to work from.
Are you lean/muscular/recently diagnosed? If so you may be very insulin sensitive and this kind of dose would make sense. On the other hand if your blood sugars are not back to normal (too high) after 4 hours it is likely that you can try a different ratio e.g. 1 unit: -4 mmol. Be conservative to avoid going too low.
Sorry to be imprecise again.

mountaintom said:

Thanks guys. It’s complicated isn’t it?! I’ve only ever dosed by 1 or 1.5 unit a time as I’m not daft enough to do more. Thanks for the advice.

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im pretty new to this myself mountaintom (a year in ) like others have said i use correction dose of 1unit drops me by 3mmol but its more like 2.5 for me as said people are different i dont like giving too many corrections and tend to most of the time correct at next meal unless unusually high but no more than 2 units hope this helps

Also to add @mountaintom If I am struggling with high BG levels and it's dry outdoors then I go and do some gardening, which seems to drop me like a ton of bricks, failing that a walk/run and stopping every 30 mins to test until I am back in range again.

Any ideas at all why you went high ?

Hi @mountaintom Eating out can be a minefield, I had what I thought was a lo carb curry 2 weeks ago, i'd eaten it at another restaurant and was fine afterwards, however I went up to about 18 mmol/l afterwards and the only reason I could fathom was that they had laced it with sugar (either that or witchcraft there too), I couldn't see why on earth it had spiked me so much, to be fair it was a rare event so did the usual waiting up all night until I could see bg levels dropping and then went to bed late but woke back in range, sometimes you really need to take a deep breath and literally say 'next'.