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From Pittsburgh, Pennsylvania, USA:

Diagnosed with type 1 four and a half months ago, my seven-year-old daughter has been using Lantus and Humalog (with a sliding scale) since her diagnosis. Now, our endocrinologist is putting her on an insulin:carbohydrate ratio including a correction factor in order to move us closer to using a pump. However, the benefit of the ratio system seems to be lost when using it for my daughter because her insulin doses are so small right now that we are unable to draw up, with accuracy, the small doses she needs. Her target blood sugar is 100 mg/dl [5.6 mmol/L] (daytime) with a sensitivity of 350 and an insulin:carbohydrate ratio of 1:45. I feel that she would benefit from moving quickly to a pump that could accommodate bolus increments as small as 0.1 units, which are impossible to draw up using a syringe. I feel that having the ability to fine tune her control with a pump would greatly benefit her. Her pediatric endocrinologist, however, says that everyone has to move from a sliding scale to the carbohydrate counting ratio system and then to a pump. Is this the standard that most endocrinologists follow? When I asked if we could dilute her Humalog so that I could more accurately draw up small doses, I was told that it probably could be done but, that they don't usually do that. Have others diluted their fast-acting insulin in order to obtain better accuracy?


Your questions are insightful and indicate that you have a good grasp (already!) of some diabetes management nuances. Good for you.

It might be helpful to learn more of your "sliding scale" so that one could understand what sort of units (or partial units) you require now to adjust your child's insulin dosage in order to get to target glucoses.

Professionally, I am a VERY firm believer that utilizing an insulin injection regimen of meal (and maybe snack) time insulin-to-carbohydrate ratios PLUS a correction factor in conjunction with the long-acting basal insulin (such as glargine/Lantus) is a superior method to prepare for insulin pumping! But, "MUST" one proceed this way? Of course not. This is how we individualize care for our patients. However, this method exactly involves the principles that pumping uses. Other clinicians certainly may have there own preferences.

Diluting insulin is a very logical consideration. It is not done as much as once was and so your healthcare provider may not be so comfortable. A loud note of caution: diluting insulin sets up you and healthcare workers (yours and any others involved in your daughter's diabetes care, including family members) for errors. If one dilutes the insulin by 50%, for example, then "1 unit" of MEASURED insulin (by "volume") only contains 1/2 unit of actual, active insulin, so you would have to give "2 measured units" in order to effectively give 1 genuine unit of insulin. Unfortunately, there have been instances where pharmacies have diluted insulin improperly and healthcare members (and patients and families) have given improper insulin doses. This really gets confusing when the insulin is diluted 25% (1 measured unit by volume = 0.25 of actual insulin) or even more dilute! So, confusion arises when one is asked to give "3.7 units of insulin" (for example): Does this mean 3.7 units of MEASURED insulin by volume or 3.7 units of total insulin? It's not impossible to overcome these extra steps, but crystal clear information is required. (3.7 units of actual insulin which is from a vial diluted 25% would be 14.8 units by volume, if my calculations are correct. If not, it underscores the potential for error here!)

There is also the problem of finding the correct material with which to dilute insulin. Some of the rapid-acting insulins have specifically recommended diluting solutions (called "diluents") that must be obtained through the manufacturer and pharmacies often have trouble obtain this. Again, not impossible but one must prepare carefully and not just "decide" one day to go to the corner drugstore and start diluting insulins.

Based on what you wrote, your daughter's formula for insulin dosing correction is: (Measured glucose minus 100) divided by 350 = number of units to give. This means that you would only be giving "extra" insulin if her glucose were 450 mg/dl [25 mmol/L] or more. You might ask your pediatric endocrinologist about slightly adjusting the target glucose upward to 120 mg/dl [6.7 mmol/L] or so. That way, if you "overshoot" the target (as you learn this process for her individual needs) you have a bit more cushion.

Finally, you wrote specifically about an insulin pump that accommodates bolus increments of 0.1 units. Before you obtain (pay for and go through insurance for) an insulin pump, be certain that you discuss consideration of an insulin pump that can provide bolus increments as low as 0.05 units (and basal increments as low as 0.025 units!).


[Editor's comment: See Diabetes Health Magazine's comparison of Insulin Pumps to learn about pumps' basal and bolus increments. BH]

Original posting 8 Mar 2010
Posted to Insulin Pumps and Daily Care


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