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Proinsulin

CPT: 84206
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Expected Turnaround Time

3 - 5 days


Related Information


Related Documents


Specimen Requirements


Specimen

Serum, frozen


Volume

0.6 mL


Minimum Volume

0.4 mL (Note: This volume does not allow for repeat testing.)


Container

Red-top tube or gel-barrier tube


Collection

Transfer the serum into a LabCorp PP transpak frozen purple tube with screw cap (LabCorp N° 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.


Storage Instructions

Freeze.


Stability Requirements

Temperature

Period

Room temperature

Unstable

Refrigerated

Unstable

Frozen

12 days

Freeze/thaw cycles

Stable x3


Patient Preparation

Baseline proinsulin levels should be collected after a 12-hour fast.


Causes for Rejection

Nonfrozen specimen; nonserum specimen; gross hemolysis; gross lipemia


Test Details


Methodology

Enzyme immunoassay (EIA)


Reference Interval

0.0−10.0 pmol/L


Additional Information

Proinsulin is synthesized in the pancreatic beta cells as a 9390 mw polypeptide of 86 amino acids.1-3 Proinsulin is subsequently cleaved enzymatically, releasing insulin into the circulation along with a residual 3000 mw fragment called C-peptide, so-named because it connects the A and B chains of insulin within the proinsulin molecule.

Proinsulin, which has relatively low biological activity (approximately 10% of insulin potency), is the major storage form of insulin. Normally, only small amounts (∼3% of the amount of insulin, on a molar basis) of proinsulin enter the circulation. Because the hepatic clearance of proinsulin is only 25% of insulin clearance, the half-life of proinsulin is two- to threefold longer and concentrations in the fasting state are approximately 10% to 15% of insulin concentrations.

High proinsulin concentrations have been associated with benign or malignant β-cell tumors of the pancreas4 and endocrine pancreatic tumors associated with MEN-1.5 Elevated proinsulin levels have been observed in individuals with impaired glucose tolerance even in the absence of abnormal glucose or C-peptide levels.6 Elevated proinsulin levels have been found to be a positive risk factor for the development on NIDDM.7,8 Most patients with β-cell tumors have increased insulin, C-peptide, and proinsulin concentrations, but occasionally only proinsulin is elevated. Despite its low biological activity, proinsulin may be increased sufficiently to produce hypoglycemia.9 In addition, a rare form of familial hyperproinsulinemia, due to impaired conversion to insulin, has been described. Increased proinsulin concentrations may also be detected in patients with chronic renal failure, cirrhosis, or hyperthyroidism.


Footnotes

1. Clark PM. Assays for insulin, proinsulin(s) and C-peptide. Ann Clin Biochem. 1999; 36(Pt 5):541-564 (review). 10505204
2. Chevenne D, Ruiz J, Lohmann L, et al. Immunoradiometric assay of human intact proinsulin applied to patients with type 2 diabetes, impaired glucose tolerance, and hyperandrogenism. Clin Chem. 1994; 40(5):754-759. 8174247
3. Bowsher RR, Wolny JD, Frank BH. A rapid and sensitive radioimmunoassay for the measurement of proinsulin in human serum. Diabetes. 1992; 41(9):1084-1088. 1499862
4. Kao PC, Taylor RL, Service FJ. Proinsulin by immunochemiluminometric assay for the diagnosis of insulinoma. J Clin Endocrinol Metab. 1994; 78(5):1048-1051. 8175958
5. Oberg K, Skogseid B. The ultimate biochemical diagnosis of endocrine pancreatic tumours in MEN-1. J Intern Med. 1998; 243(6):471-476 (review). 9681845
6. Krentz AJ, Clark PM, Cox L, et al. Hyperproinsulinaemia in impaired glucose tolerance. Clin Sci (Colch). 1993; 85(1):97-100. 8149702
7. Nijpels G, Popp-Snijders C, Kostense PJ, et al. Fasting proinsulin and 2-H postload glucose levels predict the conversion to NIDDM in subjects with impaired glucose tolerance: The Hoorn Study. Dibetologia. 1996; 39(1):113-118. 8720611
8. Porte D Jr. Normal physiology and phenotypic characterization of beta-cell function in subjects at risk for noninsulin-dependent diabetes mellitus. Diabet Med. 1996; 13(9 Suppl 6):S24-S32 (review). 8894477
9. Service FJ. Diagnostic approach to adults with hypoglycemic disorders. Endocrinol Metab Clin North Am. 1999; 28(3):519-532 (review).10500929

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
140533 Proinsulin 27882-0 140535 Proinsulin pmol/L 27882-0

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