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22796 Insulin, Free & Total (INSFT)

Insulin, Free & Total (INSFT)
Test Code: FINSUSO
Synonyms/Keywords
Free Insulin, Serum
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) 1 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

​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).

Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Clinic Laboratories
Monday through Friday​
1-3 days​
Electrochemiluminescence Immunoassay
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.

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).

Reference Range Information
​Free Insulin​2.6-24.9 mclU/mL
​Total Insulin​2.6-24.9 mclU/mL

 

Interpretation

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.

Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
83525​
​1 ​Insulin, Total, Serum
​83527 ​1 ​Insulin, Free, Serum
Synonyms/Keywords
Free Insulin, Serum
Ordering Applications
Ordering Application Description
​Centricity ​Free Insulin
​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) 1 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

​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).

Useful For
Assessing free (bioactive) insulin concentrations in patients with known or suspected insulin antibodies
Reference Range Information
​Free Insulin​2.6-24.9 mclU/mL
​Total Insulin​2.6-24.9 mclU/mL

 

Interpretation

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.

For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Mayo Clinic Laboratories
Monday through Friday​
1-3 days​
Electrochemiluminescence Immunoassay
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.