The Autobio insulin (INS) chemiluminescence immunoassay (CLIA) kit is intended for the quantitative determination of INS concentration in human serum.
Insulin is a member of structurally related regulatory proteins; other proteins in this group include the insulin-like growth factors and relaxin. Insulin is produced by the β-cells of the pancreatic islets and is initially synthesized as a 12kDa preprohormone, which undergoes intracellular processing to a 9kDa, 86-amino acid prohormone and subsequent packaging in storage granules. Within these granules, disulfide bonds are formed between the A and B chains of the insulin molecule and the C-peptide region is cleaved, resulting in the 51-amino acid, 6kDa mature insulin molecule. Upon stimulation, the islet cells release equimolar amounts of insulin and C-peptide, and small amounts of proinsulin and other intermediates(<5% of mormal total insulin secretion).
Basal and glucose-stimulated circulating insulin concentrations are relatively stable during infancy and childhood, and increase during puberty due to decreased insulin sensitivity. Insulin concentrations tend to be higher in obese individuals, particularly those with an increased proportion of visceral (abdominal) fat. Glucose counter-regulatory hormones, such as glucagons, gluconcorticoids, growth hormone and epinephrine, decrease insulin sensitivity and action; insulin levels may increase during exogenous administration of these substances.
Measurement of circulating insulin concentrations may be useful in the diagnostic evaluation of several conditions. Elevated serum insulin levels in the presence of low glucose concentrations may be indicative of pathologic hyperinsulinism, e.g. nesidioblastosis and islet-cell tumor. Elevated serum fasting insulin levels with normal or elevated glucose concentrations, and exaggerated insulin and glucose response to exogenous glucose administration are characteristic of the insulin-resistant forms of glucose intolerance and diabetes mellitus and other insulin resistant conditions. High circulating insulin concentrations may be involved in the pathogenesis of hypertension and cardiovascular disease. Conversely, low insulin concentrations in the presence of hyperglycemia suggest insulin-deficiency, e.g. insulin-dependent or Type Ⅰdiabetes mellitus. Measurement of immediate or first-phase insulin secretion after an acute glucose load may be predictive of Type I diabetes mellitus.
Endogenous anti-insulin antibodies may be observed in the prediabetic and symptomatic phases of insulin-dependent diabetes mellitus, presumably due to an autoimmune disorder. Anti-insulin antibodies are also commonly seen in insulin-treated individuals such antibodies can interfere with immunoassays for insulin, and techniques have been described to remove the antibodies prior to assay for "free" insulin. The presence of excess proinsulin and genetic insulin variants can also interfere with insulin estimations.
