Hey ,

Fasting Insulin
I usually consider fasting insulin between the 2-6 uIU/ml optimal. (The typical reference range is: 2-25)

OGTT (Oral Glucose Tolerance Test)
The glucose tolerance test (usually done with 75 gram of glucose – not with food) gives back a curve. 
• The curve is optimal when blood sugars spike in the first 30-60 minutes and return to normal after 2-2.5 hours. The highest value should not exceed the renal threshold (160-180 mg/dl). This means basically there should be no glucose in the urine afterwards.
• With early insulin resistance, we can see blood glucose drop after 2-2.5 hours below fasting levels. In this stage blood sugar levels can still appear normal, but there is already a more robust insulin response. In this stage, insulin is winning and blood glucose is dropping below fasting levels
• In a more advanced stage, blood sugars rise less quickly (the blood sugar peaks between 1-1.5 hours). The highest blood sugar level exceeds the renal threshold.  The blood glucose level does not return to normal after 2.5 hours.

Just remember that a blood glucose meter can make errors. With mild unclear values, you wouldn’t want to evaluate only one curve(Because glucose is a reflection of insulin). For that reason, I usually recommend doing an oral insulin tolerance test at the same time.

for both these tests, make sure if patients are on a ketogenic diet they raise their carb intake for a minimum of 3 days.

Fasting glucose
I consider optimal likely between 80-88 mg/dl. Above is evidence of insulin resistance.

C-peptide
I consider optimal likely between 1-2 ng/ml (with a typical reference range of 1.0-4.2). 

I hope this helps!

Hi  – you can also find all of these optimal ranges and additional information in the Blood Sugar Regulation course in the “Testing Considerations” video here.