Q: I am 23 years old and I have had insulin dependent diabetes for 9 years. My blood sugars during the day are generally under 150 mg/dl, but no matter what I do my fasting blood sugar before breakfast is always high, often over 300. What is going on?

A: The problem described above, fasting hyperglycemia (high blood sugar before breakfast), is a common complaint that vexes both patient and physician. Consistently elevated fasting blood sugars are generally due to one of the following:

1. Insufficient insulin taken the night before.

2. Somogyl Phenomenon: with this theory, it is thought that too much insulin is taken in the evening leading to unrecognized hypoglycemia in the middle of the night. The low blood sugar triggers the release of the counter-regulatory hormones (adrenaline, growth hormone, glucagon, cortisol) that increase blood sugar levels. Paradoxically, high doses of insulin taken at night lead to higher glucoses in the morning and lower doses lead to lower blood sugar levels. Although this theory had been accepted for years, currently it is controversial. Several studies have shown that lower glucoses in the middle of the night are actually associated with low glucoses in the morning and the "rebound" described above rarely occurs. This is important in that "normal" fasting glucoses may be at the expense of unrecognized hypoglycemia which can be potentially dangerous.

3. Insulin Waning: in this situation, the insulin taken the evening before has run out by morning, leading to elevated glucoses. This occurs most commonly when NPH is taken in the early evening, at 5-6 pm. This waning is the reason it is often suggested that the evening NPH be taken later at night, generally around 10 pm.

4. Dawn Phenomenon: in this situation, a predawn surge in growth hormone production leads to elevated glucose levels (yes, even long after growth has stopped). Even when there are no problems with fasting hyperglycemia, the surge in growth hormone may in part explain why more insulin is often needed before breakfast than if the same meal were eaten later in the day.

In order to determine which of the above is responsible for the fasting hyperglycemia, blood sugars must be checked at bedtime, 2 am, and the next morning. If both 2 am and morning blood sugars are high, then an increase in the evening insulin may be needed. If the 2 am blood sugars are very low and the morning blood sugars are high then the Somogyl Phenomenon may be occurring and less evening insulin may be needed. If the 2 am blood sugars are "normal" and the morning blood sugars have been high, then either insulin waning or the Dawn Phenomenon may be the cause. Insulin waning can usually be treated by moving the evening NPH to a later time. Dawn Phenomenon also may be treated by moving evening NPH to later at night, but this often will be unsuccessful. Insulin pumps are extremely helpful in this situation, as the pump can be programmed to deliver insulin at a high rate during the predawn hours. Medications that block growth hormone release have been tried, but at this point the results have been disappointing.