Insulin, Free and Total

TEST: 501561
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CPT: 83525; 83527
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Expected Turnaround Time

5 - 12 days

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Related Documents

Specimen Requirements

Specimen

Serum

Volume

3 mL (adult and pediatric)

Minimum Volume

1.5 mL (Note: This volume does not allow for repeat testing.)

Container

Red-top tube or gel-barrier tube

Collection

Submit serum in a plastic transport tube

Storage Instructions

Refrigerate.

Stability Requirements

Temperature

Period

Room temperature

2 days

Refrigerated

10 days

Frozen

200 days

Freeze/thaw cycles

Stable x6

Test Details

Use

Most patients receiving insulin will eventually form antibodies that bind insulin. These antibodies may or may not affect the activity and metabolism of insulin. Laboratory tests may be used to identify patients with insulin antibodies, for instance LabCorp test 141598. Patient antibodies may affect the normal insulin measurements. Free and total insulin is a test to measure the fraction of insulin that is bound by antibodies and to measure total insulin after the removal of antibodies by special preparation.

Free insulin represents a portion of total insulin unbound by insulin binding antibodies in the circulation. This fraction serves as a measure of biologically active insulin and provides an indication of the true relationship between insulin dose and blood glucose in diabetic patients. Levels of free insulin correlate inversely with periods of hypoglycemia or hyperglycemia in diabetic patients, where total insulin can remain fairly constant. Sequential free insulin measurements are useful to evaluate possible abnormal insulin absorption after subcutaneous injection. In this case, the presence of insulin-binding antibodies can alter the pharmacokinetics of insulin and lead to an abnormal period of hyperglycemia in response to a delayed increase in the free fraction.

Total insulin measures the sum of the antibody-bound and the free insulin fraction. It reflects both the insulin-binding capacity of circulating insulin-binding antibodies and the patient insulin dose. In patients with significant levels of antibodies, the bound fraction of insulin accounts for >90% of the total insulin. With constant insulin therapy, the total insulin levels are normally quite stable.

This test may be useful for diabetic patients treated with insulin analogs, as shown in the table below. Every patient's antibodies are different, and the specificity and avidity of the antibodies may affect the test.

Cross-reactivity of Insulin Drugs

Insulin Drug

Percentage of Cross-reactivity

Human insulin

100%

Insulin aspart

85%

Insulin glargine

92%

Insulin lispro

79%

Insulin glulisine

14%

Insulin detemir

24%

Methodology

Chemiluminescent immunometric assay (IMA) after insulin extraction of free and total insulin

References

American Diabetes Association. Standards of medical care in diabetes—2014. Diabetes Care. 2014 Jan; 37(Suppl1):S14-S80. 24357209
Merrigan SD, Owen WE, La'ulu SL, Wyness SP, Roberts WL, Straseski JA. SAT-174: Cross-reactivity of modern insulin analogs insulin detemir and insulin glulisine with six automated insulin immunoassays. 2012.
Owen WE, Roberts WL. Cross-reactivity of three recombinant insulin analogs with five commercial insulin immunoassays. Clin Chem. 2004 Jan; 50(1):257-259. 14709671
Sacks DB, Arnold M, Bakris GL, et al. Executive summary: Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem. 2011 Jun; 57(6):793-798. 21617153
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. 11238323

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
501561 Free and Total Insulin 48615-9 501563 Free Insulin uU/mL 6901-3
501561 Free and Total Insulin 48615-9 501564 Total Insulin uU/mL 20448-7

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