With a rapidly rising blood glucose level, you may choose to offset the rise with rapid-acting insulin (taking into account any active, unused insulin from previous doses) and check the monitor often to make sure your level doesn’t end up dropping too much. If your blood glucose level continues rising, you may decide to check your urine or blood for ketones. It is this type of frequent fine-tuning that can keep you within your target blood glucose range more of the time.
Both the DexCom and Medtronic systems display three-hour trend graphs on-screen (the Medtronic Guardian also displays a six-hour trend graph). Although looking back at the past three hours of data will not help you fix a problem that happened earlier in the day, it can provide you with information to prevent a recurrence of a problem.
For example, checking the three-hour trend graph a couple of hours after meals can reveal the effect of various types of food. If you have a Medtronic CGM system, you can upload your data to a Web site called Carelink, which has software that stores, organizes, and analyzes all of your numbers; the Sensor Overlay By Meal chart indicates after-meal trends very clearly. Did your blood glucose level spike very high soon after the meal? If so, perhaps you need to take your insulin earlier, get some physical activity after eating, or choose foods that digest more slowly. Did your blood glucose drop soon after the meal, and then rise a few hours later? Perhaps you need to delay your premeal insulin injection or extend the delivery of your bolus (if you use an insulin pump).
For those who inject pramlintide (brand name Symlin) or exenatide (Byetta), the three-hour trend graphs can show whether or not the medicine is effective at minimizing blood glucose spikes after meals without causing hypoglycemia. Although after-meal hypoglycemia with exenatide is rare, it is possible, especially for people who take a sulfonylurea drug such as glipizide, glyburide, or glimepiride. If hypoglycemia occurs, your doctor may reduce the dose of the sulfonylurea. Hypoglycemia after meals is more common with pramlintide. In this case, the solution may be to delay the mealtime insulin injection or to extend the insulin delivery (if using an insulin pump), or to reduce the dose of premeal insulin.
The three-hour trend graph can also reveal blood glucose patterns related to exercise. Checking the graph during and after exercise will show when and how much your blood glucose rises or falls. Insulin and snack adjustments can be made based on the patterns seen on-screen. For competitive as well as casual athletes, these adjustments can enhance performance.
Stress is another concern for many people. In some instances, stress can cause an abrupt or prolonged blood glucose rise. At other times, it can make blood glucose drop. The very inconsistency of the way stress affects blood glucose can cause, well, more stress. I have found that the three-hour trend graph provides a nice “inside look” at the effects of various forms of stress on blood glucose levels. Not only can you see if the stress is making your blood glucose rise or fall (requiring extra insulin or an immediate snack, respectively), but it can also indicate how long the effects last so that you’ll be better prepared the next time around.
The 9-hour graph on the DexCom system and the 12- and 24-hour graphs on the Guardian system (the 24-hour graph is only on the integrated CGM–pump system) play a role in the regulation of basal insulin, particularly overnight. Whether you take insulin by injection or from a pump, the basal component of your insulin program is designed to match your liver’s normal, sustained secretion of glucose into the bloodstream. In other words, the basal insulin should hold your blood glucose level steady in the absence of food, exercise, stress, or mealtime doses of rapid-acting insulin.