1. Avoid hemolysis
2. Label specimens with corresponding draw times.
3. Serum-gel tubes should be centrifuged within 2 hours of collection.
4. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.
5. Send specimen refrigerated
Additional Information: If multiple specimens are drawn, send separate order for each specimen.
Human antimouse antibodies (HAMA) may interfere with the assay.
Hemolysis interferes with this assay, as insulin-degrading peptidases are released from erythrocytes. This assay has 100% cross-reactivity with recombinant human insulin (Novolin R and Novolin N). It does not recognize other commonly used analogues of injectable insulin (ie, insulin lispro, insulin aspart, and insulin glargine).
Insulin is produced by the beta cells of the pancreas. It regulates the uptake and utilization of glucose and is also involved in protein synthesis and triglyceride storage.
Circulating insulin antibodies develop after diabetic patients are treated with exogenous insulin preparations. The presence of insulin antibodies has 2 main consequences:
1. Insulin antibodies will directly bind to insulin, making it unavailable for metabolic activity.
2. Insulin antibodies may adversely affect the binding characteristics of insulin in immunoassays, making reliable quantitation difficult.
Free (bioactive) insulin could be measured after polyethylene glycol (PEG) precipitation of insulin antibodies and their bound insulin. If insulin antibodies are not present, the free and total insulin should be equivalent. The laboratory will report results of the total insulin (without PEG precipitation) and the free insulin (with PEG precipitation).
If insulin antibodies are not present, the free and total insulin should be equivalent. A significant difference between total and free insulin is suggestive of the presence of insulin antibodies.
During prolonged fasting, when the patient's glucose is reduced to less than 40.0 mg/dL, elevated insulin level plus elevated levels of proinsulin and C-peptide suggest insulinoma.
In patients with insulin-dependent diabetes mellitus, insulin levels generally decline.
In the early stage of noninsulin-dependent diabetes mellitus (NIDDM), insulin levels are either normal or elevated.
In the late stage of NIDDM, insulin levels may also decline as levels of proinsulin decrease.