Factitious hyperinsulinemia is differentiated from insulinoma by -

Factitious hypoglycemia is the intentional attempt to induce low blood glucose levels . Factitious hypoglycemia results from exogenous self-administration of insulin or insulin secretagogues medications (e.g., sulfonylureas, meglitinides). Note that insulin-sensitizing drugs like metformin, do not cause hypoglycemia . Insulin synthesis occurs in the beta cells of the pancreas as proinsulin, which is then processed and cleaved into insulin, and C peptide held together by disulfide bonds and excreted into the circulation. Insulin will be then rapidly removed by the liver, whereas C peptide remains in the circulation for a more extended period till the kidneys clear it and the insulin to C peptide ratio in healthy individuals will be less than one. Some proinsulin molecules would also get excreted in the blood without processing, and this is still detectable in the plasma . Serum C-peptide is a marker of endogenous insulin secretion (a synthetic insulin does not contain C-peptide) and is paicularly useful if a patient is on exogenous (injected) insulin treatment, when insulin assays would simply detect the injected insulin. Serum C-peptide can help clarify the differential diagnosis of diabetes, as it is usually very low in long-standing type 1 diabetes and very high in severe insulin resistance. It is also useful in the diagnosis of spontaneous hypoglycaemia Ref - davidsons 23e p727 , pubmed.com