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HelpMayo Test ID INSFT Insulin, Free and Total, Serum
Specimen Required
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: 2.45 mL
Collection Instructions:
1. Avoid hemolysis
2. Label specimens with corresponding collection 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 collected, send separate order for each specimen.
Useful For
Assessing free (bioactive) insulin concentrations in patients with known or suspected anti-insulin antibodies
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| INSF | Insulin, Free, S | No | Yes |
| INSTO | Insulin, Total, S | Yes, (Order as INS) | Yes |
Method Name
Electrochemiluminescence Immunoassay (ECLIA)
Reporting Name
Insulin, Free and Total, SSpecimen Type
SerumSpecimen Minimum Volume
0.75 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 14 days | |
| Frozen | 180 days | ||
| Ambient | 24 hours |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | OK |
| Gross icterus | OK |
| Autopsy/postmortem specimen | Reject |
Clinical Information
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.
Some patients receiving insulin may develop antibodies that bind insulin. These antibodies may or may not affect the activity and metabolism of insulin.
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 ultrafiltration to remove anti-insulin antibodies and their bound insulin. If insulin antibodies are not present, the free and total insulin concentrations should be equivalent. The laboratory will report results of the total insulin (without ultrafiltration) and the free insulin (after ultrafiltration).
Reference Values
FREE INSULIN:
3-25 mcIU/mL
TOTAL INSULIN:
3-25 mcIU/mL
Interpretation
Free insulin represents the portion of total insulin unbound by anti-insulin antibodies in the circulation. This fraction serves as a measure of biologically active insulin and provides an indication of the true relationship between insulin and blood glucose.
Most individuals do not have anti-insulin antibodies in circulation and therefore the free and total insulin concentrations would be equivalent.
When a significant difference between total and free insulin Concentrations is observed following ultrafiltration, the result is suggestive of the presence of insulin antibodies. In these cases, confirmation of the presence of anti-insulin antibodies (Mayo Test ID: INAB) may be helpful.
Cautions
In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. The presence of antibodies to streptavidin or ruthenium can also rarely occur and may also interfere in this assay. Caution should be used in interpretation of results, and the laboratory should be alerted if the result does not correlate with the clinical presentation.
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).
Clinical Reference
1. Lupsa BC, Chong AY, Cochran EK, Soos MA, Semple RK, Gorden P. Autoimmune forms of hypoglycemia. Medicine (Baltimore). 2009;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;47(3):602-605
3. Sacks DB: Diabetes mellitus. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics 6th ed. Elsevier; 2018:1160-1200
Method Description
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. (Package insert: Insulin reagent, Roche Diagnostics; 2022)
For free insulin, specimen immunoglobulins and their bound insulin are filtered out using a centrifugal ultrafiltration device with a molecular weight cut-off of 125,000 daltons. The filtrate, containing free insulin alone, is analyzed using the method described above.
Day(s) Performed
Monday, Wednesday, Friday
Report Available
1 to 4 daysSpecimen Retention Time
14 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
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.CPT Code Information
83527-Free Insulin
83525-Total Insulin
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| INSFT | Insulin, Free and Total, S | 48615-9 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| INSTO | Insulin, Total, S | 20448-7 |
| INSF | Insulin, Free, S | 6901-3 |