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22796 Insulin, Free & Total (INSFT)

Insulin, Free & Total (INSFT)
Test Code: FINSUSO
Synonyms/Keywords
​​​Free Insulin, Serum
Test Components

​Insulin, Free

Insulin, Total

Useful For
Assessing free (bioactive) insulin concentrations in patients with known or suspected insulin antibodies
Specimen Requirements
Fasting Required Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
​Yes (8 hours) Serum​ Serum Separator Tube (SST) Red Top Tube (RTT) 2.45 mL​ 0.75 mL​
Collection Processing Instructions
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.

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.​  

Specimen Stability Information
Specimen Type Temperature Time
Serum​ ​ Refrigerate (preferred) 14 days​
Ambient 24 hours
​Frozen​180 days
Rejection Criteria
  Gross hemolysis, Autopsy/postmortem specimen
Interference

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). 

Performing Laboratory Information
Performing Location Day(s) Test Performed Report Available
Methodology/Instrumentation
Mayo Clinic Laboratories
Monday through Friday​
1-4 days​
Electrochemiluminescence Immunoassay (ICLIA)
Reference Lab
Test 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 Range Information
​Free Insulin3-25 mclU/mL
​Total Insulin3-25 mclU/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.

Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
83525​
​1 ​Insulin, Total, Serum
​83527 ​1 ​Insulin, Free, Serum
Synonyms/Keywords
​​​Free Insulin, Serum
Test Components

​Insulin, Free

Insulin, Total

Ordering Applications
Ordering Application Description
​Cerner ​Free Insulin (8128)
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Fasting Required Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
​Yes (8 hours) Serum​ Serum Separator Tube (SST) Red Top Tube (RTT) 2.45 mL​ 0.75 mL​
Collection Processing
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.

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.​  

Specimen Stability Information
Specimen Type Temperature Time
Serum​ ​ Refrigerate (preferred) 14 days​
Ambient 24 hours
​Frozen​180 days
Rejection Criteria
  Gross hemolysis, Autopsy/postmortem specimen
Interference

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). 

Useful For
Assessing free (bioactive) insulin concentrations in patients with known or suspected insulin antibodies
Test Components

​Insulin, Free

Insulin, Total

Reference Range Information
​Free Insulin3-25 mclU/mL
​Total Insulin3-25 mclU/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.

For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Report Available
Methodology/Instrumentation
Mayo Clinic Laboratories
Monday through Friday​
1-4 days​
Electrochemiluminescence Immunoassay (ICLIA)
Reference Lab
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
83525​
​1 ​Insulin, Total, Serum
​83527 ​1 ​Insulin, Free, Serum
For most current information refer to the Marshfield Laboratory online reference manual.