I am a 40 year old, mother of two, who has had type 1 diabetes for 19 years. My HbA1c levels are consistently below 6.5%, but the range of blood sugars is large. My average blood sugar is around 120 mg/dl (6.7 mmol/L) with a standard deviation of 70 mg/dl (3.9 mmol/L). Fifteen percent of my readings are below 70 mg/dl (3.9 mmol/L), but I have no problems with hypoglycemic episodes (except when I was pregnant). I use Humalog and Ultralente. I would like to know what would be an acceptable standard deviation in my situation.

There is no such thing as “acceptable” blood sugar or standard deviation. You want to aim for as close to normal as possible with the least variation (lowest standard deviation) as possible while still avoiding low blood sugars. With the same amount of effort, some people are able to get better control than others. You don’t want to try so hard for “perfect” blood sugars that you overdo it and go low very often. Even if you “feel fine” when you are below 70, I suggest you not drive when your blood sugar is that low. You may be developing hypoglycemia unawareness and may have impaired driving skills even if you feel fine.

TGL