How to use Continuous Glucose Monitors Effectively

Woman wearing glucose monitor and insulin pump
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Continuous glucose monitoring (CGM) has now been use for nearly 15 years in the clinical setting. In the past, patients generally wore devices for several days but didn’t have access to the recorded information. The information would be downloaded by a medical professional for subsequent interpretation. These days, patients usually have personal CGM technologies which allow them to see their own blood glucose levels in real time.

Yet, despite rapid advances in technology, many patients complain that it is difficult to know how to use the devices and supplied information effectively.

Here are some tips to help patients use their CGM systems to their maximum potential:

  1. Don’t forget to calibrate CGM technology with several daily finger stick glucose checks. The CGM data can’t be accurately interpreted unless this is done. The CGM sensors measure glucose levels in the interstitial fluid (the fluid that bathes and surrounds cells) rather than in blood, and this inevitably leads to a loss of accuracy. Calibration helps minimize inaccurate reporting.
  2. Even though CGM is sophisticated, it should not replace log book records. Lines on a graph are often meaningless if your doctor doesn’t know that blood sugars rose because you were at a restaurant and forgot to take your insulin or because you were stressed about an upcoming exam.
  1. Don’t forget to use event markers record exercise sessions. In addition, if possible, mark down the type of exercise performed, since aerobic exercise tends to lower blood glucose levels while anaerobic exercise can actually raise blood sugar levels.
  2. You should also note alcoholic intake including type of alcohol and amount. Alcohol initially leads to hyperglycemia due to the sugar content in the drink but may also lead to delayed hypoglycemia.
  1. Periods of illness and stress should be documented whenever possible.
  2. In my opinion, the most important information derived from CGM is the detection of recurrent overnight hypoglycemia. Low blood sugars can lead to seizures and worse and should be targeted first and foremost. One should always first try to eliminate nocturnal hypoglycemia before tackling other issues such as daytime hypoglycemic or hyperglycemic excursions.
  3. The sensor daily overlay/daily trends report shows the glucose levels for each day within a certain time period superimposed upon one another. This allows for the identification of trends which occur at the same time each day. For example, perhaps sugars are consistently rising after breakfast. This implies that the insulin to carbohydrate ratio should be increased for breakfast. Similarly, the overlay may show low blood sugars overnight every night, in which case, perhaps the basal insulin dose should be reduced.
  4. Daily summary/glucose tends report allows the user to look at each day individually to carefully assess the effects of diet, exercise, alcohol, stress and illness etc on glucose levels. Are certain meals more likely to cause hyperglycemia than others? This is obviously particularly helpful if you keep a diary so that patterns can be linked to habits (see number 2)

    Hopefully, these tips have been helpful. In the right setting, CGM can be a powerful tool for reducing hemoglobin A1C while also preventing hypoglycemia. 

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