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Insulin ratios

ArtemisBow

ArtemisBow

Well-Known Member
Messages
312
Type of diabetes
Type 1
Treatment type
Insulin
So, I recently went on the DAFNE course, and part of that involved calculating what our ratios should be for bolusing, correction etc.

The way this was done (and I've seen the same formulae used in books and so on) is to divide a number by your TDD (Total Daily Dose) - TDD being the total number of units you take each day, all your basal and boluses added together.

My question is, doesn't using this figure to work out ratios make some fairly big assumptions? Firstly, that you're taking roughly the right amount of insulin in the first place? Secondly, that we're all eating roughly the same amount of carbs? Some of the other people in my group were eating significantly more carbs than I was - if I were to eat that quantity I would take more insulin, have a bigger TDD and therefore an entirely different ratio? This is also an iterative formula in that if I used the ratio it came up with, ate the same thing again, I would now take a different amount of insulin, change my TDD and then change my ratio again.....it would just go round forever!

I tried to discuss this with the nurse running the course but she wasn't that comfortable with maths. I'm just not sure my ratio I was given was right, and as I don't have confidence in the calculation I'm not sure how to adjust correctly!
 
What they are trying to do is to work out what you need. The ratios are supposed to be calculated relative to your carb consumption, so your TDD gives you the total insulin used, but then your meal ratios give Insulin:Carb Portion ratio, which is typically iu per 10g Carbs.

e.g. You are stable and you have a TDD of 100 units, made up of 50 Basal, 50 Bolus.

Your bolus is split 15:15:20 Breakfast:Lunch:Dinner

Your breakfast is 15iu for 70g carbs - ratio 1:4.7
Your lunch is 15iu for 70g carbs - ratio 1:4.7
Your dinner is 20 iu for 80g carbs - ratio 1:4

This makes it easier to work out how much more insulin to take when you eat additional carbs or how much less to take when you eat fewer.

I do however agree that the random divide 100 by TDD to give you the required correction dose is mostly a pile of hocum.

If I went by the calc, I would have a correction dose that worked on 1u reducing my Blood glucose level by 2.4 mmol/l, however I know from experience that this number depends on where my blood sugar is and also tends to be more like 1 iu corrects for 2.8-3 mmol/l at normal levels and at elevated levels 1u is worth <2mmol/l.

I think it's a way to introduce the idea of understanding how it works, but it does require some give and take and you have to work it all out for yourself once you have a bit of experience.
 
The Rule of 100 is only a rough guide at best, but it's a starting point in which to begin.
 
I guess the issue I have is that I was using 1:10 with relative success through trial and error, but because my TDD was about 20 they said I should be using 1:25 - which I think would be totally inadequate. I guess it's only a start point, but I'm surprised they bother with the calculation in that case. Also the majority of people on the course did not have stable BG - this was why they were there.
 
1:10 is probably the avg ratio. If it was working well for you prior to DAFNE and you held good BG levels then I wouldn't consider changing it. The rationale behind DAFNE is to teach you to experiment with your insulin with confidence, both basal & bolus. It's not to force you onto a ratio that won't work.
 
ArtemisBow said:
I guess the issue I have is that I was using 1:10 with relative success through trial and error, but because my TDD was about 20 they said I should be using 1:25 - which I think would be totally inadequate. I guess it's only a start point, but I'm surprised they bother with the calculation in that case. Also the majority of people on the course did not have stable BG - this was why they were there.
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As NH adn DD have said, it's a rule of thumb, adn a starting point for your iterations to go from

At least they waited until you on the course to change your ratios.

Prior to my DAFNE course I was told to change from my 1:20 ratio to 1:10 which I flat refused to do as it would have left me with hypos after every meal. Once we'd sorted by basal out (about a 30% reduction) I changed my bolus to 1:15 on MDI, which worked well.

On the pump, my basal rate is halved (didn't need to adjust that much) but my bolus was initially 1:45 by the rules of thumb, back down to about 1:25 now, and a correction ratio of 1U:8mmol/l. I think the key point, if you read either Think Like a Pancreas or Pumping Insulin they give you methods to test all three.
 
Thanks all - I'm going to reread think like a pancreas and start on my ratios again, as my levels are all over the place and I've just been woken up by a hypo - clearly something needs adjusting!
 
I find that different times of day bring different activity levels which in turn alter ratios...

If I eat the same meal for breakfast, lunch & evening & follow my normal activity schedule, I will have to use three differing amounts of rapid acting to do the same job. I.E. Breakfast & pottering around the house = 8 units, golf after lunch = no novorapid & snacks during the round to avoid hypo, lazy evening will almost double the amount required...

add in honeymooning & so on and it can be a full time job just working it all out.

Everyone is individual & you'll work out what suits you. The course adds to your diabetes education & allows you to make better descisions for yourself.
 
ArtemisBow said:
I guess the issue I have is that I was using 1:10 with relative success through trial and error, but because my TDD was about 20 they said I should be using 1:25 - which I think would be totally inadequate. I guess it's only a start point, but I'm surprised they bother with the calculation in that case. Also the majority of people on the course did not have stable BG - this was why they were there.
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What has been used here to calculate the bolus carb ratio is the 500 rule but this is rsrely correct so in many ways, its best to use 1u to 10g and just adjust it up or down to try to get sensible bg targets.
 
My DN sensibly started me on a 1:10 ratio which most people start with. This can then be adjusted for time of day and feedback from the meter. This approach is simple and works
 
ArtemisBow said:
Thanks all - I'm going to reread think like a pancreas and start on my ratios again, as my levels are all over the place and I've just been woken up by a hypo - clearly something needs adjusting!
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It's a great book and worth reading all over again. If today's hypo is a one-off don't change things just yet, monitor your levels for the next couple of nights and see what bg levels your getting throughout the early hours, sometimes hypo's can happen for no apparent reason.
 
I just started on a 1:10 or as DAFNE put it a 1:1, which was there idea, this was a good place to start I think.......

I wonder if the advice has changed or is it just a localised decision......
 
novorapidboi26 said:
I just started on a 1:10 or as DAFNE put it a 1:1, which was there idea, this was a good place to start I think.......

I wonder if the advice has changed or is it just a localised decision......
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1 unit to 1 CP, I could never get my head round that and still count in grams.
 
tim2000s said:
When I was diagnosed, I'm pretty sure 10g of carbs was called an "exchange"....
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Yea...........I remember back in the 60's, counting my food using 10g carb exchanges to equal the amount of allowed carb st different meal times.
 
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