<Not a doctor.>
I do have insulin resistance, and I just wanted to point out that A1Cs got way too much praise and is not that great of a test. If someone has florid diabetes, it will show it, yes. (Can you use florid for diabetes?) But it sometimes misses people who are not well with insulin resistance and type 2 diabetes who are at risk for cardiovascular complications.
When the WHO adopted A1C as a biomarker for diabetes, the incidence of diabetes fell and the mortality of it rose.
Because it sometimes misses diabetes.
My A1C is always in the low to mid 5s. But I were to eat certain foods, my blood sugar can go up to 220. And it can crash down to the 70s. Normal people don't have their glucose go above 180 even when challenged with high glucose consumption, though, by OGTT definition, and by looking at actual population data it's really more 120-140 as a maximum after meals. Yet my A1C remained perfectly normal.
I have never had an A1C at 6 or above, and the WHO guideline was to diagnose at 6.5%.
People with insulin resistance have red blood cells with shorter life spans and as a result you're going to inherently have a bias toward lower A1C values. Not to mention high glycemic excursions are damaging to endothelial cells--as is the constant state of hyperinsulinemia.
The OGTT is now the gold-standard again with the WHO, but you really can find out just about as much with a home meter which have become increasingly accurate.
I had to convince my doctor to do a fasting insulin test to show him how bad my insulin resistance was because I was testing fasting and after meals and knew I had a problem, yet my A1Cs were good and it was all he was interested in. Yet the boom and bust glycemic excursions are not good for the body regardless of the A1C, and knowing your numbers can help you realize which foods cause that pattern.
Fasting insulin is a very good predictor of the development of diabetes and presence of insulin resistance, and he was surprised at my results.
Edit: I forgot to quote. This was for
@DrAmazingishere
I do agree though what you said about the end results being the same after the imaging. It was probably 20 years ago I was introduced to Dr. Amen through some TV program, and I can recall the same thing, in which he diagnosed ADHD with the aid of SPECT imaging and the end result was giving medication, the same as it would have been without the imaging.