Question from India:

My query is related to C-Peptide test interpretation which doctors generally ignore for a patient as they feel does not hold any importance. My C-Peptide at diagnosis was 390 pmol (206 – 934). I am 32 years old and often had fasting blood sugars in the 270 mg/dl [15.0 mmol/L] range. I’m unable to derive any interpretations from this.

My doctor says I have type 2, which I believe should be supported by hyperinsulinism/with insulin resistance, so my C-Peptide should be quite high. Similarly, in type 1, C-Peptide values are negligible, which again is not supported. Also, I was not very overweight nor lean, with a BMI of 27 before diagnosis

I have several questions. If my fasting C-Peptide is 390 pmol (206 – 934), what does this signify in a diabetic patient as beta cells will be working in the bolus mode at a sugar level of 270 mg/dl [15.0 mmol/L]?

Another point is that persistent blood glucose levels over 150 mg/dl [8.3 mmol/L] contribute to glucose desensitization/toxicity which will not reflect true C-Peptide. Should I get my C-Peptide level tested again to know the real values? After three months of insulin initially, I’m on metformin 500, twice a day, and exercise, with fasting blood sugars of 80 mg/dl [4.4 mmol/L] to 100 mg/dl [5.6 mmol/L] and postprandial blood sugars no higher than 140 mg/dl [7.8 mmol/L] for seven months.

Is C-Peptide a predictor that the subject will be insulin dependent in future? If that is, then which data should I look upon, C-Peptide at diagnosis or after treatment? Otherwise, my GAD Antibodies are -ve, but I have not been tested for ICA/IAA 2. What do you suggest?