1-SST/1 mL serum. After 30 minutes of clotting, promptly centrifuge and refrigerate.
ALTERNATE SPECIMEN: PLASMA–HEPARIN (SODIUM OR LITHIUM)
Refrigerated 7 days
Evaluate insulin producing neoplasm (islet cell tumor, insulinoma) or pancreatic islet cell hyperplasia; work-up for hypoglycemia to evaluate insulin production in diabetes mellitus. Insulin-secreting tumors usually present with hypoglycemic symptoms and are diagnosed by a 72-hour prolonged fast. After 72 hours of fasting an insulin concentration greater than 6 mU/L indicates an insulinoma. Factitious hypoglycemia from exogenous insulin shows increased insulin, but not proinsulin or C-peptide.