Can a C-Peptide test can determine if production of insulin is natural from the pancreas or supplied only by insulin injection? Or, what kind of test can determine how much insulin is still produced naturally by the pancreas and how much is supplied “externally?” What is the minimum level of naturally produced insulin to cover all needs?

The C-Peptide test indicates how much insulin is coming from the body. Insulin that is injected has virtually no C-Peptide. Therefore, this is a blood test that can distinguish between externally administered insulin or bodily produced (endogenous) insulin. If somebody has a high insulin level, nobody could tell from where the insulin was coming, but with a high insulin level and a low C-Peptide, it must be coming from external sources, i.e., injection. In legal terms, this could “prove” that somebody had insulin injected as a cause of severe hypoglycemia or even hypoglycemia-induced coma and death. It could also point the way towards an insulin-producing tumor where both insulin and C-Peptide levels would be elevated disproportionately. There is no absolute C-Peptide level that indicates insulin sufficiency, however, so the insulin to glucose ratios must be interpreted semi-quantitatively by an experienced endocrinologist.

SB