Quantitative Insulin Analysis Using Liquid Chromatography–Tandem Mass Spectrometry in a High-Throughput Clinical Laboratory

Abstract

BACKGROUND Circulating insulin concentrations reflect the amount of endogenous insulin produced by the pancreas and can be monitored to check for insulin resistance. Insulin is commonly measured using immunochemiluminometric assays (ICMA). Unfortunately, differing crossreactivities of the various ICMA antibodies have led to variability in assay results. In contrast, liquid chromatography–tandem mass spectrometry (LC-MS/MS)-based approaches can provide a highly specific alternative to immunoassays. METHODS Insulin was extracted from patient serum and reduced to liberate the insulin B chain. Subsequent resolution of the peptide was achieved by LC coupled to triple-quadrupole MS. Selected-reaction monitoring of B-chain transitions was used for quantification. Recombinant human insulin was used as a calibrator and was compared against the National Institute for Biological Standards and Control (NIBSC) reference standard. Bovine insulin and a stable isotopic-labeled (13C/15N) human insulin B chain were used and compared as internal standards. RESULTS The LC-MS/MS assay described herein has been validated according to CLIA guidelines with a limit of detection of 1.8 μIU/mL (10.8 pmol/L) and a limit of quantitation of 3 μIU/mL (18.0 pmol/L). A correlation between the LC-MS/MS assay and a US Food and Drug Administration-approved ICMA was completed for patient samples and the resulting Deming regression revealed good agreement. A reference interval for the assay was established. CONCLUSIONS A simple, high-throughput, quantitative LC-MS/MS insulin assay traceable to the NIBSC standard has been successfully developed and validated.