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Insulin, Intact, LC/MS/MS

Test code(s) 93103

Question 1. What are the primary clinical uses of insulin testing?

Insulin testing is typically used to assist in the differential diagnosis of hyperinsulinemia and/or hypoglycemia and in the differential diagnosis of type 1 versus type 2 diabetes mellitus (DM).

Question 2. Why is the Insulin, Intact LC/MS/MS assay superior to other commercially available insulin assays?

A limitation of most commercially available insulin immunoassays is that they measure fragments of the insulin molecule. Consequently, molecules that share these fragments may cross-react and lead to an artificially high result. The Insulin, Intact, LC/MS/MS assay only measures the intact molecule, eliminating the possibility of cross-reactivity with other molecules.

Question 3. How is the Insulin, Intact LC/MS/MS assay performed?

The assay includes high-throughput immunochemical enrichment of intact insulin from serum followed by liquid chromatography-tandem mass spectrometry (LC/MS/MS). Quantitation is based on standards traceable to the WHO international reference preparation 83/500.

Question 4. Which individuals may be suitable for insulin testing?

Insulin testing may be considered in:

  • Seemingly healthy nondiabetic individuals with hypoglycemia of unknown cause
  • Individuals with diabetes of uncertain etiology (ie, autoimmune/type 1 versus nonautoimmune/type 2), including:

    – Young persons with atypical diabetes

    – Individuals with ketosis-prone diabetes that is not clearly type 1

    – Obese individuals with acute-onset diabetes with ketoacidosis

    – Lean individuals with nonketotic diabetes

  • Individuals at risk for type 2 DM (eg, those who are overweight/obese and/or have a family history of DM, a history of gestational DM, or meet the criteria for metabolic syndrome)

Question 5. What is the sensitivity and specificity of the Insulin, Intact, LC/MS/MS assay?

The analytical sensitivity is 3 µIU/mL. It is specific for intact insulin. There is no cross-reactivity with proinsulin or common insulin analogues. However, the presence of Humalog® (insulin lispro injection) in the blood specimen may preclude insulin quantitation. The presence of insulin antibodies may also cause an artificially low result. 

Question 6. How might an elevated fasting insulin level be interpreted?

Elevated fasting insulin levels may be seen in patients with insulinoma, exogenous insulin, or type 2 DM. High insulin results could also be associated with a broad range of disorders including insulin resistance, obesity, hypertension, dyslipidemia, renal failure, atherosclerosis, nonalcoholic fatty liver disease, sleep apnea, polycystic ovary syndrome, Cushing’s syndrome, acromegaly, andnesidioblastosis.1,2,3

Question 7. How might a low fasting insulin level be interpreted?

Low insulin levels may be observed in patients with type 1 DM, monogenic DM, pancreatic diabetes, and late stage type 2 DM.4,5,6

 

References
 
  1. Kelly CT, Mansoor J, Dohm GL, et al. Hyperinsulinemic syndrome: the metabolic syndrome is broader than you think. Surgery. 2014;156:405-411.
  2. Cryer PE, Axelrod L, Grossman AB, et al. Evaluation and management of adult hypoglycemic disorders: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2009;94:709-728.
  3. Resmini E, Minuto F, Colao A, et al. Secondary diabetes associated with principal endocrinopathies: the impact of new treatment modalities. Acta Diabetol. 2009;46:85-95.
  4. Handelsman Y, Bloomgarden ZT, Grunberger G, et al. American Association of Clinical Endocrinologists and American College of Endocrinology - clinical practice guidelines for developing a diabetes mellitus comprehensive care plan - 2015. Endocr Pract. 2015;21(suppl 1):1-87.
  5. Choudhuri G, Lakshmi CP, Goel A. Pancreatic diabetes. Trop Gastroenterol. 2009;30:71-75.
  6. Weir GC, Bonner-Weir S. Five stages of evolving beta-cell dysfunction during progression to diabetes. Diabetes. 2004;53(suppl 3):S16-S21.
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
Document FAQS.170 Version: 0
Effective 09/15/2015 to present