My husband, age 35, was diagnosed with type 1 diabetes about three months ago and started insulin therapy immediately. However, he had hypoglycemia several times a day until his doses were cut back to almost nothing. A recent C-peptide was 640, so now we have been told he has type 2. What does this test mean to us? Should we do other tests? several times a day until his doses were cut back to almost nothing. A recent C-peptide which was 640., so now we have been told he is a type 2. What does this test mean to us? Should we do other tests?

C-peptide is a measure of a portion of the precursor insulin molecule which is secreted. Therefore, one molecule of C-peptide is generated for every molecule of insulin secreted. In the big picture, it is a reflection of endogenous insulin secretion.

Since patients with type�1 diabetes have destruction of insulin-producing cells, they have very low levels of insulin secretion (and low C-peptide levels). On the other hand, persons with type�2 diabetes have insulin resistance and make increased amounts of insulin to compensate for the insulin resistance. I am not sure of the units for the C-peptide in your husband’s case, but presumably this is a measurable amount of C-peptide.

It is not altogether clear when patients with type 1 diabetes enter the honeymoon phase, because they can actually make insulin for a while. I would suggest having measurements of antibody (including islet cell antibodies, GAD antibodies, and anti-insulin antibodies) tests which are elevated with type 1 diabetes. Finally, you can have insulin and C-peptide measured in response to a glucose challenge. Some patients in the honeymoon phase make insulin after they recover from the high sugars, but lose their ability to make insulin rather rapidly over time. Please discuss these issues with the physician caring for your husband.

JTL

[Editor’s comment: The normal range for a fasting C-peptide level is usually 0.8-4 ng/ mL.

SS]