The acanthosis nigricans should eventually clear up, I believe. A lot of the skin conditions do.
But as mentioned, an occasional test of your fasting insulin, while useful information, is not going to give you a picture of what your insulin is doing from day to day, and certainly not from hour to hour.
The best test to determine your degree of insulin resistance would be an oral glucose tolerance test, which is both expensive and time-consuming. However, there are other markers that can be used, such as HbA1C and C-peptide, as well as your HOMA-IR score. If your HbA1C and C-peptide are good, and your inflammatory markers (WBC, CRP, ferritin, etc.) are good, then you probably don’t need to worry about your insulin level.
Also, as I might have already mentioned, testing for ketones is another good way to get an idea of what insulin is doing. If your liver is producing enough ketone bodies for you to be in what we call “nutritional ketosis,” then your insulin is definitely low enough for good metabolic health. Insulin inhibits ketogenesis, so the presence of circulating ketones, say a level of serum β-hydroxybutyrate of 0.5 mmol/L or above, tells you your serum insulin is low. In fact, Ralph De Fronzo and his team have determined that around 25 μU/mL is the cutoff point. So if you have circulating ketones, then you can be sure that your insulin is lower than 25 μU/mL.
Lowering insulin is one of the major benefits of a well-formulated ketogenic diet, but the presence of ketone bodies in the blood stream is another benefit, since they not only act as fuel for the brain, heart, and other organs, but they also have highly beneficial epigenetic effects. But as I said, ketogenesis is inhibited by insulin above 25 μU/mL, so if you have circulating ketones, you are not only benefiting from their presence, you are also benefiting from low serum glucose and low serum insulin.