Carb counting in USA and Germany

Diabetics in USA, Canada, Australia and other countries are used to count their carbohydrates in weight units. As a consequence they think in ‘Carbs per Insulin unit’ to get the dose of insulin that must be applied for a certain number of carbs. The mathmatical operation applied is a division:

Dosage(USA) = Carbs / Carbs per Insulin unit = 61 / 6.5 = 9,38 = 9 IU

Diabetics in Germany are used to think in bread units. 10g of carbs are 1 bread unit (BU). As a consequence they use the ‘Insulin factor’ that is multiplied with the number of BUs to get the dosage. So the mathmatical operation is a multiplication:

Dosage(GER) = BU * Insulin factor = 6.1 * 1.5 = 9,15 = 9 IU

Both ways have their advantages and disadvantages. It is quite obious to me that we human beings will bend the numbers a bit to make the calculation easier. This means ‘Carbs per Insulin’ will most likely be used without decimal places. The ‘Insulin factor’ on the other hand will most likely have only one decimal place and then only something like .5 that is easy to calculate with.

So in both systems the convenience of calculation will lead to calculation errors. If the real ‘Carbs per Insulin’ ratio is 6.2 and you calculate with 6.5 then the dosage will be lower than your needs. If the real ‘Insulin factor’ is 1.7 and you calculate with 1.5 you will underdose your insulin as well. The likelyhood to apply an insulin dose that is one or more units to low or to high will grow with the number of carbs. I leave it to the mathmaticians which way is more likely to cause these errors…

The team has just implemented the ‘Carb per Insulin unit’ approach. It can be used in Glucosurfer if you set your carbohydrate scale to ‘gram or other weight unit’. This was a learning process for the team and I am thankful for the input from the Tu community.