by Gary Scheiner
When it comes to managing diabetes, basal insulin gets very little respect. Most people can’t spell it correctly (basil? basul?), and even fewer know what it’s even used for. And that’s a shame, because basal insulin represents the FOUNDATION upon which insulin therapy is built.
Basal insulin’s job is to offset the liver’s secretion of glucose into the bloodstream. Everyone’s liver does it, mainly to supply the brain and nervous system with a steady supply of energy, and mainly in response to the many hormones that are in circulation.
Because the liver is secreting sugar into the bloodstream continuously, a lack of insulin would result in a sharp rise in blood sugar levels. It would also cause many of the body’s cells to starve for fuel and can cause the production of acidic “ketones” as cells turn to alternate fuel sources. And too much insulin would overwhelm the available supply of glucose in the blood and result in a blood sugar drop.
Suffice it to say that basal insulin is necessary for survival, and the right amount is critical to achieving stable blood glucose control.
Meeting Basal Needs
Each person’s basal insulin requirement is unique, affected by factors such as body size, activity level, stage of growth, hormone levels, and the amount (if any) of internal insulin production from one’s own pancreas.
During a person’s growth years (prior to age 21), basal insulin requirements tend to be heightened throughout the night. This is due to the production of large amounts of hormones (growth hormone and cortisol) that stimulate the liver to release extra glucose into the bloodstream. After the growth years, production of these hormones is reduced and limited primarily to the predawn hours. The “dawn effect”, as this is called, results in an increased secretion of glucose by the liver in the early morning. Thus, basal insulin requirements in most adults tend to peak during the early morning hours.
Using intermediate insulin (NPH) at night to meet basal needs can often result in hypoglycemia during the night (as the insulin “peaks” 4-8 hours after injection), and a blood glucose rise in the evening as the NPH wears off. Long-acting/basal insulins (Lantus and Levemir) are relatively flat and peakless, meaning that there may not be enough basal insulin during the night and early morning, and there may be too much in the afternoon and evening.
Pump therapy is unique because it offers a great degree of maneuverability in terms of matching basal insulin to the body’s needs. Basal insulin is made up of small pulses of rapid-acting insulin every few minutes. The rate of delivery (the “basal rate”) can be adjusted hourly, if needed, to match the liver’s normal 24-hour pattern of glucose secretion.
Pumps also permit temporary changes to basal insulin at a moment’s notice. This can come in handy during periods of extended physical activity or very low activity (such as during travel). It can also be used to improve control during illness, menstrual cycle changes, stressful situations, alcohol consumption (which can produce a prolonged drop in blood sugar levels), and following very high-fat meals.
Setting Basal Doses
In most cases, the daily (24-hour) dose of basal insulin nearly equals or is slightly less than the daily mealtime insulin. This depends on a person’s body weight and sensitivity to insulin, which is affected greatly by physical activity. The bigger you are, the more basal insulin you will need. The more active you are, the less you will need. During a person’s growth/teen years, basal insulin needs can be particularly high. In advanced age, basal insulin needs can be quite low.
When evaluating basal insulin levels, keep this important fact in mind: in the absence of food, exercise and mealtime/bolus insulin, basal insulin should hold the blood sugar fairly steady.
It is a good idea to fine-tune your pump’s basal insulin settings before settling on specific bolus doses or insulin-to-carb ratios to use at mealtimes. When high or low blood sugars appear, it is difficult to know what to adjust unless the proper basal insulin levels have already been established.
To test the your basal insulin settings, you will need to wait approximately 4 hours after your last bolus and meal/snack. This will give the carbs time to finish digesting and the bolus time to finish working. The meal (or snack) eaten before the test should be fairly low in fat (no restaurant food or take-out) in order to avoid a delayed blood sugar 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 the onset of menses, following hypoglycemia, or if the blood sugar is greater than 250 at the beginning of the test.
To start the test:
• Check your blood sugar about four hours after the last bolus
• If the blood sugar is above 250, bolus for the high blood sugar and cancel the test
• If below 80, eat to bring your blood sugar up and cancel the test
• If the blood sugar is not too high or too low, proceed with the test
• Check your blood sugar every hour or two until you next usual mealtime
If your blood sugar drops by more than 30 mg/dl during the test period, the basal rate is probably too high. If it rises by more than 30 mg/dl, the rate may be too low. The basal rate should be changed in increments of .05 to .2 units/hr depending on your usual settings and the magnitude of the rise or drop that took place. The next day, re-test to see whether the adjustment produces a steadier blood glucose level. Continue to adjust and re-test until steady blood glucose levels are obtained.
Note that basal rates are usually changed one hour prior to an observed rise or fall in the blood sugar, since the rapid-acting insulin infused by the pump takes about an hour to peak. For example, if your blood sugar rises between 3 a.m. and 7 a.m., you would increase the basal rate between 2 a.m. and 6 a.m.
A Little Perspective…
Having the right basal insulin program and setting the right doses is important for anyone who uses insulin. Receiving too much basal insulin, or receiving it at the wrong times, can result in frequent (and perhaps severe) hypoglycemia, not to mention weight gain. Receiving too little basal insulin will produce high blood sugars and make it very difficult to set appropriate mealtime bolus doses. Insulin pumps allow the greatest degree of precision in setting basal insulin levels, and that can produce the best control and lifestyle flexibility.
Fine-tuning basal insulin can be complex. Don’t hesitate to reach out to a member of your health care team who specializes in this sort of thing.
Gary Scheiner MS, CDE is a diabetes educator with a private practice (Integrated Diabetes Services) near Philadelphia, and author of Think Like A Pancreas: A Practical Guide to Managing Diabetes With Insulin. He has had Type-1 diabetes for 20 years, and offers diabetes education and management consultations via phone, fax, and Internet to patients throughout the world. Submit inquiries to firstname.lastname@example.org, or call (877) SELF-MGT.