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Assessing free (bioactive) insulin concentrations in patients with known or suspected insulin antibodies
Patients treated with exogenous insulin preparations might develop autoantibodies against insulin.
If significant differences between the total and free insulin concentrations are detected, the presence of insulin antibodies is suspected.
Test Id | Reporting Name | Available Separately | Always Performed |
---|---|---|---|
INSF | Insulin, Free, S | No | Yes |
INSTO | Insulin, Total, S | Yes, (Order as INS) | Yes |
Electrochemiluminescence Immunoassay (ECLIA)
Free Insulin, Serum
Serum
Patient Preparation:
1. Fasting (8 hours)
2. For 12 hours before specimen collection do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions:
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.
0.75 mL
Gross hemolysis | Reject |
Gross lipemia | OK |
Autopsy/postmortem specimen | Reject |
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum | Refrigerated (preferred) | 14 days | |
Frozen | 180 days | ||
Ambient | 24 hours |
Assessing free (bioactive) insulin concentrations in patients with known or suspected insulin antibodies
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).
FREE INSULIN:
2.6-24.9 mcIU/mL
TOTAL INSULIN:
2.6-24.9 mcIU/mL
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.
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).
1. Lupsa BC, Chong AY, Cochran EK, Soos MA, Semple RK, Gorden P: Autoimmune forms of hypoglycemia. Medicine (Baltimore). 2009 May;88(3):141-153
2. Sapin R, Le Galudec V, Gasser F, Pinget M, Grucker D: Elecsys insulin assay: free insulin determination and the absence of cross-reactivity with insulin lispro. Clin Chem. 2001 Mar;47(3):602-605
The Roche Cobas insulin method is a sandwich electrochemiluminescence immunoassay that employs a biotinylated monoclonal insulin-specific antibody and a monoclonal insulin-specific antibody. Insulin in the specimen reacts with both the biotinylated monoclonal insulin-specific antibody (mouse) and the monoclonal insulin-specific antibody (mouse) labeled with a ruthenium complex, forming a sandwich complex. Streptavidin-coated microparticles are added and an interaction occurs between the biotin and streptavidin, binding the complex to the solid phase. The mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed with ProCell. Application of voltage to the electrode induces the chemiluminescent emission, which is then measured.
For free insulin, specimen immunoglobulins are precipitated by adding an equal volume of 25% polyethylene glycol (PEG). The precipitate is removed by centrifugation and the supernatant analyzed using the method described above.(Package insert: Roche Insulin reagent, Roche Diagnostics; 2013)
Monday through Thursday
This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
83527-Free Insulin
83525-Total Insulin
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
INSFT | Insulin, Free and Total, S | 48615-9 |
Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
---|---|---|
INSTO | Insulin, Total, S | 20448-7 |
INSF | Insulin, Free, S | 6901-3 |
Change Type | Effective Date |
---|---|
Test Status - Test Down | 2023-01-24 |
Test Changes - Specimen Information | 2021-10-21 |