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March 1, 2009

Daily Care, Other

Question from Coeur D'Alene, Idaho, USA:

I just needed some information on calculating negative insulin orders. My patient had a recent change in orders which included a “negative” insulin order for every 50 mg/dl [2.8 mmol/L] below 150 mg/dl [8.3 mmol/L]. Right now, my supervisor is working through this with me but I would like to have extra help to make sure I’m getting it right. This is how I have been calculating it: I have been taking his blood sugar before breakfast and lunch. If it is below his target of 120 mg/dl [6.7 mmol/L], he gets no insulin. If it’s below 100 mg/dl [5.6 mmol/L], I start with a negative 1 order so the patient would get zero insulin. Then, I wait until he eats and count the amount of carbohydrates he eats and add that to his negative number, which the order says is one-half unit per every 20 grams of carbohydrates. Example, a blood sugar of 83 mg/dl [4.6 mmol/L] = -1. If he eats 50 grams of carbohydrates, I take 50 divided by 20 divided by 2 to get 1.25 units. Then, I subtract 1 for the negative order and come up with 0.25 units of insulin. This patient is highly autistic and cannot tell us if his sugars are low, or if he just feels off, so this is really important. Any help would be much appreciated.


From: DTeam Staff

I’m not sure I understand exactly what you are trying to convey, but let me see if this is close.

We’ll start by assuming that the child’s order for rapid-acting insulin (Humalog, NovoLog, or Apidra), includes the “correction” formula of (Measured Blood Glucose – Target Blood Glucose) and this value is divided by a “sensitivity factor.” In addition, he is supposed to get one-half unit of rapid-acting insulin for every 20 grams of carbohydrates that he ingests at meals and snacks. In the example you gave, it would appear that the child’s target glucose is 120 mg/dl [6.7 mmol/L] and the sensitivity factor is 50 mg/dl [2.8 mmol/L]. I am a bit confused because at one point you infer that the target is 150 mg/dl [8.3 mmol/L] and another time you suggest “negative” dosing for values under 100 mg/dl [5.6 mmol/L].

So, this is what I think you should be doing, assuming that the target glucose and sensitivity factors I noted were indeed correct:

Let’s say the child’s glucose is 247 mg/dl [13.7 mmol/L] before a meal AND he is about to eat (or has just eaten) 53 grams of carbohydrates. If he is supposed to get one-half unit of rapid-acting insulin for each 20 grams, then the insulin dose for the food is 1.3 units (I’d round to 1.5 units). [0.5 times 53 divided by 20 equals 1.3]. To correct for the high glucose of 247 mg/dl [13.7 mmol/L], he would also get 2.5 units of rapid-acting. [247 minus 120 = 127. 127 divided by 50 is 2.5] So, his total insulin dose for this meal would be about 1.5 plus 2.5 = 4 units.

What if his actual glucose were 83 mg/dl before that same meal? Then, you would calculate the correction as (83 minus 120) = negative 37. Negative 37 divided by 50 is 0.75. So, in this scenario, his total dose for the meal would be 1.5 units for the food eaten (53 grams) subtract 0.75 units for a total of 0.75 units.

While some families and physicians will give “negative insulin” (as you say), I typically do not! Why? Because most of the time, I find that people underestimate carbohydrate intake at meals. However, if this is what were prescribed, then this would be what you should do.

I find it easiest for nursing less familiar with these basal-bolus insulin plans to carefully write out the formulas [(Measure glucose – Target glucose) divided by sensitivity factor] and the insulin-to-carbohydrate ratio (1/2 unit per 20 grams) each time and then add them up.

Additional comments from Michelle Noschese:
I am not a fan of the negative orders, but that is how our hospital does it, too. So, yes, you are right. A more simplified way of saying it is to take the insulin dose (for carbohydrates) and then it gets adjusted up or down based on the premeal blood sugar value. However, it seems pretty complex for use in a hospital or institutional type setting and I bet it would be prone to errors.