The determination of insulin in serum is primarily used for the diagnosis of glycemic disorders in diabetic and pre-diabetic patients in the assessment of insulin resistant syndromes. Insulin is synthesized by the pancreatic beta cell as a precursor, proinsulin. Proinsulin is processed to insulin and C-peptide, a contiguous peptide between the insulin A and B chains, as it passes through the cell. The C-peptide in the proinsulin ensures correct folding and processing of proinsulin as it passes through the cell. Both insulin and C-peptide are released together from the beta cells in response to increased glucose levels. Because of differences in half-life and hepatic clearance, peripheral blood levels of C-peptide and insulin are no longer equimolar but remain highly correlated. A steady-state plasma glucose test in individuals undergoing an insulin suppression test to assess insulin resistance found that the combination of insulin and C-peptide was a better indicator of insulin resistance than either one individually.
Specimen Sources
Blood, ArterialBlood, CapillaryBlood, Central LineBlood, Venous
Specimen Types
Blood
Container
Gold Top Tube
Collection Instructions
Container/Tube: Gold Top Tube or Red Top Tube Specimen: 0.5 mL serum ( 0.3 mL min) Transport Temperature: Refrigerated Note: Overnight fasting is required
Transport Instructions
Refrigerated
Specimen Stability
1 day Room Temperature 7 Days Refrigerated 28 Days Frozen
Methodology
Immunocapture Liquid Chromatography/Tandem Mass Spectrometry
