April 2, 2001
Blood Tests and Insulin Injections, Honeymoon
Question from Lyndhurst, New Jersey, USA:
My son was diagnosed with type 1 diabetes about a year and one-half ago, and has a C-peptide test done at his three-month visits. His non-fasting values range from 1.6 to 1.8 Can you please tell me the reason for a a C-peptide? What does the test determine? Does this mean he is still in his honeymoon period?
Once someone has started on insulin nowadays, it is nearly always human insulin. This means that if you measure insulin levels in the blood you cant tell if it is insulin that is still being made in a child’s own islet cells or whether it is injected insulin. The way around this is to do a C-peptide test, which is a fragment of the precursor to insulin (proinsulin) that the body makes and is split off before the insulin itself is secreted. There is none of this peptide in commercial insulin preparations so that it a way of assessing whether the honeymoon period is continuing.