Laboratory: Clinical Biochemistry
Test Name:
Test Code: MISC
Clinical Information:
Proinsulin is the major storage form of insulin and is cleaved to form C-peptide and insulin. Only small amounts of proinsulin enter the circulation. High proinsulin concentrations are found in patients with beta-cell tumors of the pancreas. Occasionally, only proinsulin is increased due to defective conversion of proinsulin to insulin. Measurement of proinsulin is helpful in the differential diagnosis of suspected beta-cell tumors in patients with hypoglycemia but levels of C-peptide and insulin that are not elevated.

To avoid misdiagnosis, proinsulin measurements used in the diagnosis workup of patients with hypoglycemia must be interpreted in the context of coexisting illness, blood glucose level at time of sampling, and other test results (ie. insulin, C-peptide & sulfonylurea drug screen).
Collection Devices:
Collect in ice cooled lavender top EDTA.  Collect fasting specimen, place on ice immediately following draw and send to laboratory without delay.
Specimen Required:

Plasma: 1.0 mL
Reference Values:
Within 2 Weeks
See Also:
More Information:
Ensure whole blood has chilled on ice for at least 10 minutes, then spin down in a refrigerated centrifuge.  Transfer plasma in a polypropylene vial.  Store and send frozen to Mayo Medical Laboratories.  Mayo Test ID:  PINS/80908