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April 6, 2001

Blood Tests and Insulin Injections

Question from Chicago, Illinois, USA:

I am 30 years old, was diagnosed with type 1 diabetes a year ago, and my control has been excellent with very little insulin (before breakfast: 3 units of Humalog and 8 units of NPH; dinner: 3 units of Humalog and 3 units of NPH). Recently, my non-fasting C-peptide was 3.6. How reliable is the C-Peptide test? Based on this information, how much, if any, insulin is my pancreas is producing?

Answer:

C-peptide represents a portion of the precursor hormone which is cleaved away as insulin is secreted. Therefore, a molecule of C-peptide represents a molecule of insulin secreted. It is a good test to evaluate residual insulin secretion. It is best interpreted with a simultaneous glucose to determine whether there is adequate insulin secretion for a given level of blood sugar. Your level clearly indicates you have residual insulin secretion left. Based on what you have told me, I cannot determine whether you have type 1 or type 2 diabetes.

The small amount of insulin you are taking is consistent with type 1 diabetes, good insulin sensitivity, and residual insulin secretion. For patients with Late-onset Autoimmune Diabetes of Adulthood (LADA), the onset is more insidious with progressive beta cell loss. It is almost as if you are in a protracted honeymoon phase.

Keep it up. The best way to prolong the honeymoon phase is to maintain the good blood sugar control.

JTL