The ambulatory glucose profile: What, why, and how?
Once only available for a select group of people with diabetes using continuous glucose monitoring (CGM), the ambulatory glucose profile (AGP) is now being utilized worldwide by hundreds of thousands of individuals with diabetes and their clinicians to analyze blood glucose monitoring results. So what exactly is an AGP? Why is it now being more widely used? And how does it help? This article will provide answers to these questions and more.
Drawbacks to existing approaches and the need for change
Glucose levels have traditionally been self-measured with a finger stick and glucose meter, a process referred to as self-monitoring of blood glucose (SMBG). CGM devices have evolved the paradigm through the use of a sensor placed in the interstitial fluid that measures and reports the blood glucose concentration as often as every 5 minutes for approximately 7 days (the labeled length of use of most sensors). While both SMBG and CGM provide benefits, they also pose certain challenges. For instance, SMBG is unable to capture enough data points to tell a complete story of daily glucose control, partially because of human behavior (ie, testing frequency and adherence to recommended testing patterns); while with CGM, the challenge can be the production of too much data.
Using glucose monitoring to effect therapeutic and lifestyle changes is a collaborative effort between individuals living with diabetes and their healthcare team. In practice, this typically involves the person with diabetes responding to their blood glucose result at the time of checking by making changes to their food, activity, or medication (most specifically insulin). It is often only during a routine visit with their diabetes care team or when they are struggling with levels of glucose control—whether too high or too low—that all of a patient’s recent blood glucose results (SMBG or CGM) are reviewed for patterns, a process referred to as pattern management .
Glycated hemoglobin (HbA1c) does not capture the highs and lows from the day, or the patterns in glucose levels. As a result, HbA1c alone does not provide enough information to make treatment decisions, especially when suspecting hypoglycemia or hyperglycemia.
Simplifying and standardizing pattern management
Effective use of glucose data is challenging for healthcare professionals who have not been trained to identify glucose patterns, something which is often hampered by the recording method used. If glucose readings are not recorded in an organized/recognizable fashion, interpretation of the trends in the data can become much more difficult. This can be addressed, somewhat, through the use of software that facilitates the download and interpretation of glucose meter readings. Unfortunately this approach is hampered by being time-consuming, not always readily available in all clinics, and lacking standardization. Further complications include inadequate provision of information, poor knowledge regarding the meaning of the results, and an inability to identify appropriate adjustments based on the results.
For many healthcare providers, the challenges of working with SMBG/CGM data have reinforced the practice of making therapeutic decisions by glycated hemoglobin (HbA1c) values alone. HbA1c does not capture the highs and lows from the day, or the patterns in glucose levels. As a result, HbA1c alone does not provide enough information to make treatment decisions, especially when suspecting hypoglycemia or hyperglycemia.
From inception to realization
The AGP was first discussed in a paper published in 1987 . Over the following 3 decades, as software evolved and demonstrated relevance to clinical practice, several more publications describing its clinical utility became available . A more recent paper, published in 2013, presents recommendations for the standardization of glucose reporting and analysis in order to optimize diabetes care . In the past few years, AGP software has been made available through web-based diabetes management systems such as diasend® (Glooko, Inc., Mountain View, California, USA), and through flash glucose monitoring (FGM) devices, which include the relevant software as part of the reader. More than 30 years since it was first discussed, I strongly believe that the time has come for AGP.
A visual tool to aid clinical decision making
The AGP is a visual report that converts all of the readings obtained from CGM and FGM into a waveform. While the waveform will start to develop after 5 days of data collection, 14 days of data collection has been deemed ideal to most accurately reflect glucose control . The end result of converting the numbers into a waveform is a graph as illustrated below. This makes interpreting blood glucose levels much easier for both trained and untrained users .
An example of an ambulatory glucose profile report.
The graph above demonstrates what is reported when the software has a sufficient number of glucose readings. It shows a median glucose control line; the 25th to 75th percentiles, which represents 50% of the glucose readings over the analysis time period (typically 14 days); and the 10th to 90th percentiles, which helps the user to identify any outliers that are contributing to the median result.
AGP software changes the results from numbers on a page, or lines on a graph in the case of CGM, into a result that can help the user to quickly identify areas of concern, including hypoglycemia or potential hypoglycemia, overall glucose control (now thought of as “time in range”) and mean blood glucose value, and the degree of glycemic variability the individual is experiencing.
... being able to recognize potential hypoglycemia, overall time in range, and glycemic variability in one chart can change the conversation during a patient’s visit very quickly.
While the potential contribution of glycemic variability to the development of diabetic complications is still under debate , addressing glycemic variability is highly important to the prevention of hypoglycemia, with high glycemic variability increasing its risk. More importantly, being able to recognize potential hypoglycemia, overall time in range, and glycemic variability in one chart can change the conversation during a patient’s visit very quickly. Trouble spots are easy to identify, and strategies to remedy these, such as lifestyle changes or medication adjustments, can then be made. When necessary, if an actual glucose value on the graph is deemed to be important enough to be discussed, this can still be accessed through the CGM or FGM device. For example, this might be particularly important when looking at hypoglycemic events and understanding precipitating factors.
Is a picture worth a thousand words?
Utilization of the AGP provides patterns that can be addressed at a glance, and changes the conversation between the patient and healthcare team in the clinic. By removing the need to make sense of the numbers on the page or multiple graph lines, the waveform produced by the AGP highlights areas to be addressed while having the patients’ own target levels act as the reference. While the time in range may vary between patients, their targets are their own. This type of pictorial display, while facilitating analysis by the healthcare team, is very easy for patients to understand. With good self-management skills, patients can also identify and implement the necessary changes whether lifestyle or medication adjustment. So yes, a picture is worth a thousand words.
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