Since I first started working with diabetes patients about 17 years ago, it has been drilled into me that a low blood sugar should be treated with 15 g of carbohydrate. Over the years, I have often questioned this “Rule of 15”. Why 15 g? Why not 10g or 20g? The “science” behind this recommendation was never really explained to me. Does it really apply to everyone and every situation of mild hypoglycemia? It seems that some people end up with rebound hyperglycemia after treating with 15 g carbohydrate. Where did the Rule of 15 come from? Does it work for everyone? Is there something better?
In 1993, a group of researchers investigated a model of insulin-induced hypoglycemia in a group of people with type 1 diabetes. They found that 10 g of oral glucose raised plasma glucose levels from 60 to 97 mg/dl over 30 minutes; the levels started to decrease again after 60 minutes and reached pretreatment levels in 2 hours. Twenty grams of oral glucose raised plasma glucose levels from 58 to 122 mg/dl over 45 minutes, with a greater response at 15 minutes; again, the levels started to decrease after 60 minutes and approached pretreatment levels after 2 hours. In this same study, injected glucagon increased plasma glucose levels to 212 mg/dl in about 60 minutes with a return to pretreatment levels after about 3–4 hours. The researchers, Weithop and Cryer, concluded that in the case of persistent or recurrent hypoglycemia, although oral glucose is effective, it is a temporary solution, and subsequent consumption of a more substantial snack or meal may be required. This early research by Weithop and Cryer, as well as early observations in the DCCT, may well have been the source for the “Rule of 15.”
The Rule of 15 recommends treating a blood glucose < 70 mg/dl by eating or drinking 15 g of quick carbohydrate and repeating this treatment if the blood glucose remains low after 15 minutes. However, I was recently reading “Pumping Insulin” by Walsh and Roberts which describes a different algorithm for treating hypoglycemia based on an individual’s body weight. They suggest treating a low with 1 g carbohydrate for each 10 lb of body weight. For example, a person weighing 150 lb would treat with 15 g, but a person weighing 250 lb would need to treat with 25 g of carb. For the person on an insulin pump, they also suggest consuming additional carbs for any bolus insulin on board by taking the on board units multiplied times the person’s correction factor. For example, if a 130 lb person has 2 units on board with a correction factor of 12, they would treat the low with 13 g + 24 g carb for a total of 37 g carb. The insulin on board adjustment makes a lot of sense, but the treatment based on the person’s body weight seems that it could lead to overtreatment of low blood glucose and rebound hyperglycemia in individuals at higher body weights. This also raises questions about what, if any, other treatment strategies are being used or recommended. Could it be the treatment of hypoglycemia is like so much of diabetes in that one size does not fit all? What does this mean for future diabetes education?
What are your thoughts?