To determine whether your overnight basal insulin dose is set correctly, try the following:
1. Have a fairly healthy dinner that does not contain a great deal of fat. Avoid restaurant or take-out food before this test. High-fat food will cause a prolonged blood glucose rise and will contaminate the test results. Take your usual doses of dinnertime and nighttime insulin.
2. If you normally exercise in the evening, go ahead and do so, but keep the intensity and duration modest. Very heavy exercise may cause blood glucose to drop several hours later, which would also contaminate the test.
3. At least three hours after dinner, perform a bedtime blood glucose check. As long as your blood glucose level is above 80 mg/dl and below 250 mg/dl, do not eat any food or take any rapid-acting insulin. If your blood glucose level is below 80 mg/dl, have a snack and try the test another night. If it’s above 250 mg/dl, give a correction dose of insulin and try again another night.
4. If your blood glucose level was above 80 mg/dl and below 250 mg/dl and you have decided to go ahead with the basal insulin test, check your blood glucose again in the middle of the night (or the middle of your sleep time) and again when you first wake up the next day. The middle-of-the-night reading is needed to rule out the Somogyi phenomenon, in which low blood glucose causes “rebound” high blood glucose.
If your blood glucose remains within 30 mg/dl from bedtime to wake-up time, your basal dose is probably OK. If it rises more than 30 mg/dl, increase your basal insulin dose by 10% and repeat the test. If it drops by more than 30 mg/dl, decrease your basal insulin by 10% and repeat the test. Continue adjusting and repeating the test until your blood glucose holds reasonably steady through the night.
For example, if your bedtime reading was 185 mg/dl and your wake-up reading was 122 mg/dl, your basal insulin dose is too high, because your blood glucose dropped by 63 mg/dl while you slept. Had your bedtime blood glucose level been closer to normal, you would have experienced hypoglycemia during the night. Reduce your basal insulin dose by 10%, and run the test again the following night. Had your blood glucose risen from 87 mg/dl to 160 mg/dl — a rise of 73 mg/dl — an increase in your basal insulin dose would be in order. If your bedtime reading was 95 mg/dl and you woke up at 87 mg/dl, your basal insulin dose would not need to be adjusted because your blood glucose level changed by only 8 mg/dl.
Fine-tuning pump basal rates
Appropriate basal rates must be established to obtain quality blood glucose control and enjoy the flexible lifestyle afforded by an insulin pump. Remember: The right basal rate is one that keeps your blood glucose at a fairly constant level when you have not eaten or taken a bolus dose for several hours and are not exercising.
To test your basal insulin settings, you will need to wait approximately four hours after your last bolus and meal or snack. This will give the carbohydrates in your food time to finish digesting and the bolus dose time to finish working. The meal (or snack) eaten before the test should be fairly low in fat (no restaurant or take-out food) so that you don’t have a delayed blood glucose rise. You must stay connected to the pump continuously during the test and go about your normal, daily activities. However, heavy exercise should be avoided during the fasting phase of the test. Testing should not be performed during an illness or onset of menses, following hypoglycemia, or if your blood glucose level is greater than 250 mg/dl at the beginning of the test. (See “Insulin Pump Basal Rate Testing Schedule.”)