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Low fasting insulin and rising glucose



I have recently lost 35 pounds after starting thyroid replacement - have been exercising more also - I was not obese before - just overweight and relatively small waist, normal cholesterol and bp. have eaten whole food diet, very little sweets, only complex carbs (whole grain) - yet at times I get feelings in the head that feel like they have to do with food or hunger while really not having much of an appetite in general. I always had fasting blood sugar in the 80`s until about 6 months ago when it went up to 99, 100, 101 and 99 again recently when I also had fasting insulin checked. the fasting insulin was about 4.6 with a range of normal at least 6. I wouldn`t be concerned except for these glucose levels that are higher then I`ve ever had - and this after the weight loss. My brother has type 2 diabetes but has been obese for years. No one else in my family has had it that I know of. I have had both types of autoimmune thyroid disease for years and am 58 years old. Should I be concerned? I can`t seem to find an answer anywhere.


I don't know that I can answer your question but I can try to raise some issues for you to think about and perhaps raise with your doctor.

First, we don't make diagnoses of diabetes on the basis of fingerstick glucose measurements - the standard criteria are based on laboratory sugars which are much more accurate - you didn't specify whether the numbers given were from a clinical laboratory or from fingersticks. A rise in fasting lab sugars in the range that you mentioned bears looking into further; it is at the threshold for so-called "impaired fasting glucose" which is category where the risk/likelihood of diabetes is greater.

Second, people with autoimmune thyroid disease have a higher frequency of autoimmune (type 1) diabetes than people without autoimmune thyroid disease, although the frequency is not terribly high. It would make a difference whether you really had to work hard to get those pounds off - or whether they came off more easily than you expected. If they did come off too easily, I would feel more compelled to make sure that you did not have an insulin-deficient form of diabetes, like type 1. I don't have enough information about your body weight, family history or other elements that would help me to sort out some of your risks.

Third, I don't know why the insulin level was done, what lab it was done in, what units the results are in - and would be a little cautious in its interpretation. The context in which it was drawn is very important for the interpretation, including the accompanying blood glucose, the timing and composition of the most recent meal and what the timing was relative to your recent weight loss. I (and most other diabetes specialists) don't use blood insulin levels routinely in the diagnosis or care of most people with diabetes - there are really only limited circumstances where it tells me something I don't already know.

The depth and nature of the questions that you are asking suggests to me that you need to see a physician who can answer these questions in a fashion that is more tailored to your own circumstances.

For more information:

Go to the Diabetes health topic, where you can:

Response by:

Robert M Cohen, MD Robert M Cohen, MD
Professor of Clinical Medicine
College of Medicine
University of Cincinnati