Interpretive Handbook
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Test 81728:
Insulin, Free, Serum
Clinical Information 
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Insulin is a hormone produced by the beta cells of the pancreas.
Free insulin measurements should be comparable to routine insulin values in the absence of insulin antibodies.
Insulin autoantibodies may develop, however, in patients who have been injecting non human insulin for treatment of insulin-dependent diabetes. These antibodies will directly bind to insulin, making it unavailable for metabolic activity. The antibodies may also adversely affect the binding characteristics of insulin in immunoassays, making reliable quantitation difficult.
Useful For Suggests clinical disorders or settings where the test may be helpful
Management of diabetes mellitus when the patient has known insulin autoantibodies
Interpretation Provides information to assist in interpretation of the test results
During prolonged fasting, when the patient's glucose is reduced to <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.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
1.4-14 micro IU/mL
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Lassman-Vague V, Belicar P, Alessis C, et al: Insulin kinetics in type I diabetic patients treated by continuous intraperitoneal insulin infusion: influence of anti-insulin antibodies. Diabet Med 1996; 13(12):1051-1055
2. Hanning I, Home P, Alberti K: Measurement of free insulin concentrations: the influence of the timing of extraction of insulin antibodies. Diabetologia 1985;28(11):831-835
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