Assessment of Circulating Insulin Using Mass Spectrometry During Insulin Glargine Treatment in Type 2 Diabetes: Implications for Estimating Insulin Sensitivity and β-cell Function

Document Type

Journal Article

Publication Date



Diabetes, obesity & metabolism




HOMA; immunoassay; insulin analogs; insulin sensitivity; oral glucose tolerance test; type 2 diabetes; β-cell function


AIMS: Given the potential effect of cross-reactivity of insulin glargine U-100 and its metabolites in the insulin immunoassay, we determined the impact on insulin sensitivity and β-cell measures in GRADE participants with type 2 diabetes receiving the analog. MATERIALS AND METHODS: Using liquid chromatography mass spectrometry (LC-MS), we measured concentrations of endogenous insulin, glargine, and its two metabolites (M1 and M2) in fasting and OGTT-stimulated plasma from 19 participants and fasting specimens from another 97 participants 12 months after randomization to receive the insulin glargine. The last dose of glargine was administered before 10:00 pm the night before. Insulin was also measured on these specimens using an immunoassay. We used fasting specimens to calculate insulin sensitivity (HOMA2-S%; QUIKI index, PREDIM index) and β-cell function (HOMA2-B%). Using specimens following glucose ingestion, we calculated insulin sensitivity (Matsuda ISI[comp] index) and β-cell response (insulinogenic index [IGI], and total incremental insulin response [iAUC] / iAUC glucose). RESULTS: In plasma, glargine was metabolized to form the M1 and M2 metabolites that were quantifiable by LC-MS; however, the analog and its metabolites cross-reacted <100% in the insulin immunoassay. This incomplete cross-reactivity resulted in a systematic bias of fasting based measures. In contrast, as M1 and M2 did not change following glucose ingestion, a bias was not observed for IGI and iAUC insulin. CONCLUSIONS: Despite glargine metabolites being detected in the insulin immunoassay, dynamic insulin responses can be used to assess β-cell responsiveness. However, given the cross-reactivity of the glargine metabolites in the insulin immunoassay, fasting-based measures of insulin sensitivity and β-cell function are biased. This article is protected by copyright. All rights reserved.


Biostatistics and Bioinformatics