My endo recently mentioned in an email that the area under the curve should be calculated for the insulin and glucose measurements from my OGTT and compared to normal. Can anyone tell me at the "Statistics for Dummies" level what this means and how AUC is used in diabetes management and research?
I have wondered about the AUC number for a while. The Medtronic CGM uses it but I don't get what exactly it means. Perhaps it has something in the manual but it doesn't seem to have "caught on" in the DOC as I hardly ever see anyone mentioning anything about it. It says AUC High 1.8 AUC Low 1.0 but I have no idea what that means or how to use it. Good thread! I hope someone turns up who knows the answer!
Believe it or not most of the doctors are uncomfortable working with math and calculus too :-). Area under the curve = "the integral".
Area under curve for insulin dose, you might be more familiar with as "Total Daily Dose". This is what you get if you integrate or sum the insulin dose over the whole day.
Area under curve for blood glucose, this is what you or I or the docs think of as "average bg". Hemoglobin A1C is essentially an average over past several months bg heavily weighted over the past 2 to 4 weeks (actually this is the bg curve convoluted with the curve of lifetime of a blood cell ... typical red blood cells only last for a month or so, but some blood conditions like anemia can distort this blood cell lifetime curve and mess up the usual assumptions over the convolution integral).
Area under the curve for the OGTT, this is not averaged over the month or more of an A1C, but is typically just the sum of all the "excess bg" over the hours after the glucose tolerance tests where they are taking your bg.
Being a full-blown T1 diabetic for almost all my life I can always play that card to get out of OGTT's. OGTT = "Oral Glucose Tolerance Test". My wife had to through those when she was pregnant. I think if I had to drink that much syrup my bg's would go way above 1000!!!
Some googling turned up "typical graphs" for response to OGTT.
Note how they say bg only goes up to 200 for a T1 diabetic? No way, I saw the syrup they made my wife drink for her OGTT, it would put me over 1000 easy. Not sure where you are in your diagnosis but making a T1 undergo an OGTT, that sounds cruel, I know that I'd have to go to the emergency room after such a test if I didn't chase it with insulin.
Thanks Tim. We asked to have my insulin also tested during my OGTT to get more info since my diagnosis is not clear. My glucose showed impaired (I have better control in the morning for some reason, the other day I topped 250 after lunch when I snacked on 2 little packets of gummy fruits) but my insulin was very low showing no first phase response with a graphed line that is typical for a T1 diabetic. My endo is a researcher at a teaching hospital so he’s fairly open to looking at many parameters but he also adheres to the ADA guidelines for diagnosis and I am still outside that box despite many symptoms and high post prandials.
Lilli D - Thanks for questioning the concept of "area under the curve." Since I like to read studies about diabetes and blood glucose control, the AUC term is often tossed in with no embedded definition. It's simply understood that the reader knows what "area under the curve" means. I am of the opinion that even complex technical writing owes it to all its readers to define its terms. A simple three sentence explanation with perhaps a link to source that explains in more detail would make these papers more accessible.
Your commenters have helped me get a better understanding of this term. I learned way back in grade school that area was the product of length x width. The answer was usually stated in "square inches."
In a typical graph of blood glucose over time the BG traces an irregular curve that doesn't permit grade school analysis of simple width (BG) x time (length). I have seen this concept explained as simply breaking up the irregularly curved area into very small slices or rectangles. When all of these very small rectangles (area) are added together the sum is the "area under the curve." I watched a youtube video on the Kahn Academy that described the concept.
The mathematical tool best suited for this measurement is the integral from calculus.