I first came across the term "ambulatory glucose profile" in a study published in 2013. While other sites charge a fee for the full text article, the site I linked to makes it available, in full, for free. It was originally published in the Journal of Diabetes Science and Technology.
Dexcom Clarity, as of June 3, 2017, has made the AGP a part of its web-based software. I applaud this development. I sure wish, however that they'd let the user customize the targeted BG range. (See correction in the comments.) I see my hypoglycemia threshold at 65 mg/dl (3.6) instead of the fixed 70 mg/dL (3.9). This report uses the upper end of the target range at 180 mg/dL (10 mmol/L) while I set mine much lower.
I know that some people abhor graphs and the number side of diabetes, but I urge you to gain at least a passing awareness of this report as I suspect it is in the process of becoming a standard clinical tool. The next time you see it may be in your endo's office. The beautiful thing about this one-page report is the the clinician and patient can together look at this data-dense report and quickly extract useful and actionable information in a visually simple way.
While the ambulatory glucose profile is an odd name, the concept is relatively simple. The study suggests that the 14-day period "standard day," is the ideal amount of time to look at and make treatment decisions and changes going forward. Fewer days may exaggerate the effect of some data outliers while longer periods can obscure significant trends.
A standard day displays in a 24-hour format on the x-axis and blood glucose levels on the y-axis. A 14-day standard day will combine all the data by hour of the day showing the median (50th percentile) as well as other percentile levels determined by individual reports. The AGP report I write about here uses the 10th, 25th, 50th, 75th, and 90th percentiles. Here's an example from the study cited above.
The green dashed lines represent the 10th percentile (lower line) and 90th percentile (upper line). The dark blue lines mark the 25th percentile (lower line) and 75th percentile (upper line). The bright orange line is the 50th percentile, aka median. The left y-axis is mg/dL and the right y-axis is mmol/L.
Diasend also features the same standardized AGP report.
So, how can we use this report to alter our treatment decisions?
For instance, without dependence on numbers, formulas, or derived indices, clinicians and patients can quickly become skilled at identifying the risk of hypoglycemia. For example, if the 10th percentile curve crosses 70 mg/dL [3.9 mmol/L] or lower, there is moderate risk of hypoglycemia at that time because consistently 10% of the values fall in this range. However, if the 25th percentile curve crosses into hypoglycemia, this implies a marked risk because more than 25% of the glucose values fall in the hypoglycemic range, and consequently this should be addressed before additional therapy is instituted to treat accompanying hyperglycemia as is often seen with significant GV [glycemia variability]. [emphasis added]
In the example above, it's easily seen that the 10th and 25th percentile dashed lines cross below the 70 mg/dL (3.89 mmol/L) at about 1:00 a.m. while the 10th percentile line crosses again just after 4:00 p.m. The early morning low is the more important of the two to address. This suggest examining any factors that can cause these lows. It might be overdosing for evening snacks or a too-aggressive pump basal rate. The late afternoon propensity to dive low could be exercise related or too much lunch insulin or a too aggressive basal rate.
The beauty of the AGP report is that it can visually call your attention to the time of day that needs action and also suggests corrective factors to consider. The same exercise can be done with analyzing hyperglycemia using the 90th and 75th percentile. The width of the blue section describes the 25th to 75th percentile. It can be quickly understood that squeezing these two lines together by reducing BG variability is highly desirable. It confirmed for me the utility of carb-linited eating.
I've also used this graph and the above cited paragraph to persuade a hypo-phobic clinician that my 10th percentile line crossing my hypoglycemia threshold is not a hair-on-fire metabolic emergency, it simply means that there is a "moderate" risk of hypoglycemia. If, however, my 25th percentile line crosses this threshold, then, according to this studies' authors, I now am at marked risk of hypoglycemia at this time of day.
I found the below AGP interesting. It was derived from data gathered from a small set of gluco-normal people. I find it interesting that even in the non-diabetic, the 10th percentile of blood glucose trends below 70 mg/dL from about 4:00 to 8:00 a.m. Pointing out this fact to my then endocrinologist made her realize that she needs to allow me this same excursion without her duty to warn me!
Congrats to Dexcom's continued improvement of it's Clarity program!
Edited to add the link to the full study for free. See first paragraph.