Insulin, Free and Total

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Turnaround Time: 5 - 12 days
CPT Code:

83525, 83527

Test Type: 3 mL (adult and pediatric), Serum
Stability Time:



Room temperature

2 days


10 days


200 days

Freeze/thaw cycles

Stable x6


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.

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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. PubMed 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. PubMed 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. PubMed 11238323

Collection Details:

Collection Instructions:

Red-top tube or gel-barrier tube.

Submit serum in a plastic transport tube.