Can someone explain I:C ratios quickly to me?

Hi everybody,

when I was diagnosed recently I was put on a low bolus regime – 1 Unit of fast acting insulin for every 20 g (2 KU) of carbs, or my "factor" was 0.5 (half a unit of insulin for every 10g of carbs) – I m from Germany so I am not familiar with the I:C ratio term. So in my case would my I:C ration be 1:20 ? Is that how it works? Thank you for enlightening me ;))

You are correct...;-)

Your carb ratio = how many carbs 1 unit of insulin will cover and lower/keep your BG on/in target. Everyone is diffrent and my I:C changes through out the day, it is related to my insulin sensitivity. In the old days we related insulin to a food exchange which I exchange = 15 gr/carbs and know that has been replaced buy. Carb counting and calculating the dose based on a I:C. which has proven to be light years ahead of the old food exchange method.

You are completely correct about your I:C ratio, it is how many grams of carbs are covered by 1 unit of insulin to keep your blood sugar normal. My morning I:C ratio is 1:5, afternoons 1:9 and dinner is 1:10. But there is also something called your ISF or insulin sensitivity factor. Or some people call it a "correction factor". It is how much your blood sugar will drop with 1 unit of insulin. My correction factors are quite different from my I:C and also change throughout the day. Morning is 1:25, lunch is 1:32 and dinner is 1:50. So if I get up in the morning and my blood sugar is say 150mg/dl and I am planning on eating 20 grams of carbs then my morning dose of insulin will be 6 units, 4 units for the food, and 2 units for the correction to get back to my target blood sugar of 100. Everyone is different and as a newly diagnosed D, your insulin needs will change as you come off the honeymoon period. Just keep an eye on your blood sugars you already seem to know a lot more than most D's in the early going.

I would also add that I consider the I:C ratio as the amount of insulin that will reach my target at 3-5 hours after the meal (not 2 hours).

Yes, your I:C ratio is 1:20, Julez, one unit for every 20 carbs. But in general, what your doctor puts you on is just a starting place. You have to get it right through trial and error and good record keeping. So let's say you use the 1:20 and at your two hour test for dinner you are always high? then you would want to try increasing it to 1:18 for a couple days and see if that works better. If you are using 1:20 and see a pattern of lows, then you can decrease (the amount of insulin) by changing your I:C to 1:22 and see how that works. Most likely you will have a different ratio for each meal, so look for patterns by each meal. (Mine are 1:5, 1:10 and 1:18). Always look for patterns, don't just change it after one high or one low. Then keep the new number for at least 3 days and again look for patterns.

Thank you Zoe for your (as always) incredibly helpful reply! This seems a very sensible way of trial and error. I have one question though: With a ratio of, say 1:18, to keep it accurate, do you make sure you have always either exactly 18g, or 36g or 54g of carbs, so you can inject either 1, 2 or 3 units of insulin? Or do you have the option of injecting half units?

I'm on a pump, Julez, so I can bolus the exact amount for the carbs. For example for my weekend breakfast this morning I bolused 3.80; for dinner last night 1.95. When I was on MDI I didn't really eat in exact multiples but just rounded off my bolus. I usually rounded it up if I was a little on the high side or down if the reverse, but it isn't an exact science. One of the reasons I love my pump!

You could though try and eat in multiples to make bolusing more exact, or get a 1/2 unit syringe.

In Germany we use the exchange unit called bread or carbohydrate unit. One BE is 10g of carbs. This number is multiplied with the carb factor to get the bolus dosage.

In USA the carbs are measured in gram. This is divided by the number of carbs covered by one unit of insulin (I:C) and this will result in the bolus dosage.

In our Glucosurfer project you can switch from I:C to BE. This will calculate the factors from I:C to BE and vice versa. This is possible because both ways show mathmatically the same thing. They are only presented differently.

Just go to my settings and switch the carbohydrates from BE to Gramm to see my factors represented as I:C

I would not connect the I:C with any target. Let me explain why.

The I:C is just meant to cover the carbs in your meal. You should reach the same blood glucose after 3-5 hours you have now. This means if you are at 190mg/dl before you are eating you will also be at 190mg/dl after 3-5 hours. It needs an additional correction to reach your target. So I would add the correction to the bolus to aim for both: coverage of the meal, correction to my target. This separation of bolus for carbs and bolus for corrections is very important in my opinion.

You can have the same success with exchanges. To multiply an exchange for carbs with a factor OR divide the gram by your I:C will result in the same dosage. The problem was that in the exchange times they used the sliding scale to determine the bolus.

In the US we used the food exchange system and some diabetics just went ahead and shot them selves, the system gave you nightmares, was inaccurate, unpredictable ,hard to understand and plan meals.

The amount of exchanges you can have each day depends on your caloric needs. If you typically consume around 1,500 calories per day, you can have eight exchanges of starch, five meat, three vegetable, three fruit, two milk and three fat exchanges. Following a 2,000-calorie diet allows you to have 11 starch exchanges, eight meat, four vegetable, three fruit, two milk and four fat you can see it was a high carb low fat diet.

I thought you just meant the US exchange unit that is equal to 15g of carbs. I was not aware that this exchange system was associated with a complete system of calorie intake and so forth.

Yes and they just weighed us and said how much insulin to dose. If we went low they said we where Bridle and if we where high they said we where not eating the right size was barbaric compared to todays carb counting.

Oh yes the good old days !

It is funny. One user requested for our Glucosurfer that we should support 15g exchange units as well. It seems that some people still like to use these units.