Insulin, Intact, LC/MS/MS

Insulin measurement is primarily used to evaluate the cause of hypoglycemia. Inappropriately elevated insulin in blood (hyperinsulinemia) is associated with hypoglycemia.¹

Hyperinsulinemia can also be associated with disorders linked to hyperglycemia, such as metabolic syndrome.² For assessment of hyperinsulinemia due to suspected insulin resistance, consider using CardioIQ^® Insulin Resistance Panel with Score (test code 36509), which includes LC/MS/MS measurements of insulin, C-peptide, and calculated IR risk.

A limitation of most commercially available insulin assays is that they react not only with intact insulin, but also with fragments of the insulin molecule. This can lead to artificially high results. Quest Diagnostics offers the Insulin, Intact, LC/MS/MS (liquid chromatography-tandem mass spectrometry) assay (test code 93103), which measures only the intact insulin molecule.³ Insulin (test code 561) immunoassay can be used to evaluate the etiology of hypo- or hyperglycemia, but it is not equivalent to the LC/MS/MS test.

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 World Health Organization (WHO) international reference preparation 83/500.

The analytical sensitivity is 3 µIU/mL and the analytical specificity provides no cross-reactivity with proinsulin nor insulin analogs aspart and degludec. Insulin analogs lispro and glargine may interfere with insulin quantitation. The presence of insulin antibodies may alter the test result. 

Elevated fasting insulin levels (>16 µU/mL) may be seen in patients with insulinoma, exogenous insulin, or type 2 diabetes mellitus (DM). Elevated insulin results could also be associated with a broad range of disorders including insulin resistance, obesity, hypertension, dyslipidemia, renal failure, atherosclerosis, sleep apnea, polycystic ovary syndrome, Cushing syndrome, noninsulinoma pancreatogenous hypoglycemia, acromegaly, Post-RYGB hypoglycemia and nesidioblastosis.^4,5

For patients without known diabetes, a fasting insulin level >10 µU/mL is consistent with the presence of hepatic steatosis. For these patients, consider further evaluation to assess the presence and stage of nonalcoholic fatty liver disease (NAFLD).⁵