Diabetes Forecast

Why Does a C-Peptide Test Matter?

I've used an insulin pump for 4 1/2 years (and been insulin dependent for 24 years). After I turned 65, Medicare was paying for my insulin and pump supplies. Recently, though, Medicare denied payment, saying my C-peptide level doesn't meet its criteria. Why does Medicare use a C-peptide test to make this decision? Russell Young, Morton, Illinois

Jill Weisenberger, MS, RD, CDE, responds: The goal of an insulin pump is to mimic the insulin secretion patterns of a person without diabetes. Insulin pumps help people with diabetes achieve tight blood glucose control, which helps prevent some of the complications of diabetes.

What to Know: Medicare covers the cost of using a pump only for people with proven type 1 diabetes or those whose insulin production is extremely low. Measuring C-peptide helps doctors determine how much insulin your pancreas produces. The insulin that comes from your pancreas starts off as a larger molecule called proinsulin. Proinsulin then splits into two pieces: insulin and C-peptide. Low C-peptide suggests there is little insulin production. Having no C-peptide indicates that you produce no insulin. (The insulin you inject or get with your pump is not associated with C-peptide.) It appears that Medicare denied coverage of the cost of your pump supplies because you produce more insulin than meets the criteria for use of a pump.

Possible Solutions: As you know from the time before you had a pump, multiple daily injections (MDI) of insulin can also mimic a healthy pancreas. MDI requires that you take a long-acting insulin to provide some insulin 24 hours per day. Additionally, you will take rapid-acting insulin with meals and perhaps with snacks. Just as you adjust the amount of insulin your pump delivers, you can adjust the amount of rapid-acting insulin you inject to match your food intake. Many people, however, find a pump much more convenient and precise.

You might also ask your physician about taking another measure of your C-peptide level. It's possible that there was a laboratory error. Also, as your diabetes progresses, your C-peptide level may decrease.

Takeaways: Blood glucose control delays the onset and slows the progression of eye, nerve, and kidney damage. Either MDI or an insulin pump should allow you to achieve similar blood sugar levels. Medicare, of course, prefers the lower-cost insulin therapy, which is MDI.



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