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Endocrine Procedures: CGM
Interpretation of CGM
Interpretation of CGM
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Video Transcription
My name is Hugo Torres. I am a second year endocrinology fellow at the University of California at Los Angeles. And I'm gonna talk about how to interpret CGM. I have no disclosures. So how to interpret CGM. Continuous glucose monitors provide a large amount of minute by minute glucose data. Analyzing the CGM reports provide actionable advice to patients requires a systematic approach. Two values provide an overview of glycemic control. The average glucose level, which averages all the glucose measurements for the time period, typically two weeks, and the glucose management indicator, GMI, which is a correlate to the hemoglobin A1c. The time and range statistics give a percentage of time that the patient spends in the desired glucose range, hyperglycemic or hypoglycemic. For most patients, the acceptable range is at 70 to 180 milligrams per deciliter, or 3.9 to 10 millimoles per liter. Some patients may need different ranges depending on their glucose management goals. Glycemic variability is an indication of how wide the variation in glucose levels is. In other words, does the patient stay fairly steady or does she change abruptly from high to low values? The lower the variability, the more stable and less labile the patient's glucose values, which is desirable. Glycemic variability may also be defined via standard deviation in some reports. There are some standardized CGM metrics that are used to determine the patient's glycemic control. These are the recommended goals for the metrics described in the previous slides. The number of days the CGM is worn and percentage of time CGM is active are important to note. For example, if the patient has issues with the sensor, then the rest of the data that is analyzed might be unreliable because it is incomplete. It is recommended that at least 70% of the data be available to have valid interpretations of the information. The mean glucose and GMI goals are individualized for each patient depending on comorbidities, hypoglycemia risk, et cetera. For most patients, the A1c goal is less than 7% and a mean glucose of about 150 milligrams per deciliter or 8.3 millimoles per liter. The glycemic variability target is less than 36%. Less variability means fewer swings from high to low glucose levels. The time above range goals are less than 25% for the high range, which is above 180 milligrams per deciliter or 10 millimoles per liter and less than 5% for the very high range, which is greater than 250 milligrams per deciliter or 13.9 millimoles per liter. Time in range of 70 to 180 milligrams per deciliter or 3.9 to 10 millimoles per liter, the goal is about 70% of the time for most patients. The time below range quantifies the patient's hypoglycemia and less than 5% of time at a glucose of 54 to 69 milligrams per deciliter or three to 3.8 millimoles per liter is recommended. Less than 1% of the time should be spent below 54 milligrams per deciliter or three millimoles per liter. We recommend you consult the international consensus guideline referenced below at the bottom for further review of other populations, such as the older adult with diabetes or pregnancy. This is what an ambulatory glucose profile or AGP report looks like. This will typically be the first page of the printout with the patient's CGM data that you will use in clinic. Other pages have day-by-day glucose patterns and other useful data. The numbers we discussed in the previous slides can all be found on the AGP. The blue box shows the CGM use statistics. Note the days worn and percent the CGM is active. The orange box demonstrates the average glucose and variability numbers. What do you think about this patient's glucose variability? The green box shows the time and range data. How would you counsel this patient about his or her time and range? Notice that the very high percentage is 20%. The high percentage is 23%. Target range is 47% with a low range of 4% and very low range of 6%. These are international consensus guidelines for time and range data for different populations. In the previous slides, we discussed general guidelines for type 1 and type 2 diabetes patients. However, we see that for older high-risk patients, pregnant patients with type 1 diabetes or pregnant patients with gestational or type 2 diabetes, the goals are different. Not only the time and range goals, but also the target ranges are different. For example, for pregnant type 1 diabetes patients, the target range is 63 to 140, not 70 to 180. That is because we want a tighter glucose control during pregnancy. For older and high-risk adults, we see that the target ranges are the same as the general population. However, the percentage goals are different. We tolerate less hypoglycemia in the older high-risk population and more mild hyperglycemia. Next, some glucose monitors will show trend arrows. Trend arrows tell the patient the current rate of change of the glucose level for the past 30 minutes. This allows the patient to see not just what the glucose level is at a given point in time, but also the direction it is predicted to go for the next 30 minutes. That way, patients can make corrections using real-time data and avoid severe highs or lows. This requires a further level of education for the patient. More detailed information on using trend arrows for management can be found at the link provided on this slide, which is from a paper by Ziegler et al., Therapy Adjustments Based on Trend Arrows Using Continuous Glucose Monitoring Systems.
Video Summary
The video features Hugo Torres, a second-year endocrinology fellow at the University of California, Los Angeles, discussing how to interpret continuous glucose monitors (CGMs). He explains that CGMs provide minute-by-minute glucose data and analyzing CGM reports requires a systematic approach. Two key values to assess glycemic control are average glucose level and glucose management indicator (GMI), which correlates to hemoglobin A1c. Time in range statistics reveal the percentage of time a patient spends in the desired glucose range. The video also covers guidelines for glycemic variability, days CGM is worn, mean glucose and GMI goals, time above and below range, and the importance of trend arrow indicators.
Keywords
continuous glucose monitors
glycemic control
average glucose level
time in range statistics
trend arrow indicators
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