Bad Math

[Cyborg]

I am trying to understand the results of my pump calculations.

I woke up low this morning (47).

I immediately ate a breakfast bar (15g carb). So I proceed to enter values into my pump to make sure I take just the amount of insulin under these conditions:

I:C = 5
Carbs = 15
BG = 47
ISF = 16

The suggested insulin dose was 0.95 units.

Then I started thinking that when I'm that low, my ISF may be much higher. So, I reenter the settings as:

I:C = 5
Carbs = 15
BG = 47
ISF = 22 (thinking I'm more sensitive to insulin at the low bg value)

The pump then suggests 1.5 units of insulin!

I'm confused... :hmmmm:

[duck]

Hmmm...What's your target blood glucose value?

[Cyborg]

In both cases, my target was 80. I truely think this is a flaw in the Animas firmware...

[johgn]

In both cases, my target was 80. I truely think this is a flaw in the Animas firmware...

If it was you could just do it again and get the same result.

[whoami]

um... something wrong with the logic in this math?

15 g / 5 = 3 units

80 - 47 = 33 that you have to bring your sugar up by..

33/16 = 2.0625 .. which means 3 - 2.0625 = 0.95

but

33/22 = 1.5 .. which means 3 - 1.5 = 1.5

isn't this right?

[Scratch]

I am trying to understand the results of my pump calculations.

I woke up low this morning (47).

I immediately ate a breakfast bar (15g carb). So I proceed to enter values into my pump to make sure I take just the amount of insulin under these conditions:

I:C = 5
Carbs = 15
BG = 47
ISF = 16

The suggested insulin dose was 0.95 units.

Then I started thinking that when I'm that low, my ISF may be much higher. So, I reenter the settings as:

I:C = 5
Carbs = 15
BG = 47
ISF = 22 (thinking I'm more sensitive to insulin at the low bg value)

The pump then suggests 1.5 units of insulin!

I'm confused... :hmmmm:

I believe if you adjust the insulin sensitivity factor, the pump is also going to calculate that carbs will have a greater effect upon your blood sugar too.

You I:C is 5 units, and ISF is 16 mg/dl. This means that 5 carbs will raise your blood sugar 16 mg/dl. 47 + 48 (3 sets of 5 carb units * 16) = expected blood sugar of 95 mg/dl.

So what happens if we use your adjustment?

47 + 66 = 113 mg/dl. To get back to 80, you need to drop 33 mg/dl. 33/22 = 1.5

[Scratch]

So yeah, if you change just the ISF without altering the I:C ratio, you'll see what looks wrong to you. If your ISF is higher when your blood sugar is low, then your I:C ratio will change as well. For example, let's say you change your I:C ratio to 1:7.5 along with different ISF of 22:

Now we've got 2 units of carbs (15/7.5) raising your blood sugar a total of 44 mg/dl for an end result of 91 mg/dl. To get back to 80, 11/22 would equal .5 units of insulin necessary.

Does all that make sense?

[JediSkipdogg]

Correct on the above 3 posts.

[xMenace]

I think I have it now.

I was a bit confused by your I:C. To me an I:C is how many units of insulin it takes to cover carbs. I usually express it in the format 1:10. I didn't know whether the simple value of 5 was 5u per 10g or 10g/2u. I now assume it's the later based on the posts and my calcs. I get the same numbers as Scratch.

It looks to me like your pump calculates insulin to cover carbs based on the I:C and the insulin to adjust BGs based on the ISF. In reality this is hogwash. Both are measures of insulin sensitivty. You can't have two different sensitivities at the same time.

I:C to ISF Conversion

10g carbs raise bgs by 50 mg/dl.

2u:10g = 25 ISF
ISF = 50 / I * C/10
ISF = 50 / 2 * 10/10
ISF = 25

[dgrilli]

We should have this post as a Sticky so when it happens to us we can review and review.

Wow what did you feel like Mike at 47?

I have a fear of taking a free tour so I was always running a little high but in the past couple of weeks I have moved my target to 110.

So what was the feeling like when you first woke up?

[Cyborg]

My head is spinning from that math!

It just seemed to me that if I was more sensitive to insulin at the lower bg value, then less insulin would be needed to cover any extra carbs not covered by the low. :hmmmm:

I felt ok at the 47. I probably would have woken up earlier if I hadn't taken a pain killer before I went to bed. Since my bg is usually very close to target, I seem to handle the lows very well. I always sleep with glucose next to me, but I felt well enough to get up and check before correcting. In fact, I felt well enough to eat a breakfast bar instead of treating with glucose, something I rarely do...