Linearization of the Disposition Index equation allows evaluation of secretion-sensitivity coupling slopes

Kieren J. Mather, Melinda Chen, Tamara S. Hannon

Research output: Contribution to journalArticle

Abstract

Aims: The Disposition Index (DI) is widely used in clinical studies of β-cell function. However, direct physiologic interpretation of the DI value and the inverse exponential slope relating insulin secretion and insulin sensitivity terms is difficult. We evaluated a linearization of the relationship that allows separate evaluation of the DI term and the slope. Methods: Insulin secretion and sensitivity indices were derived from standardized oral glucose tolerance testing, including commonly used terms and model-derived terms. The population included participants with normoglycemia, dysglycemia or Type 2 diabetes. Logarithmic transformation of the DI equation to linearize the secretion-sensitivity relationship was performed, and the resulting secretion-sensitivity relationships were evaluated using standard linear regression methods. Results: Simple logarithmic transformation linearized the secretion-sensitivity relationships available from a variety of OGTT-derived metrics. In normoglycemic subjects the slopes approximated −1 in insulin-basedsecretion-sensitivity pairs, and approximated −0.6 in C-peptide based secretion-sensitivity pairs. Group differences in DI terms were observed as expected. These analyses also revealed differing secretion-sensitivity slopes, with IGT and T2D demonstrating progressively impaired coupling. Conclusions: Linearization of the secretion-sensitivity relationship provides simplified interpretation of the DI value and allows simple analysis and meaningful interpretation of the secretion-sensitivity slope. This linear relationship is amenable to standard statistical evaluations for comparisons of insulin secretion responses and of secretion-sensitivity coupling across groups.

Original languageEnglish (US)
Article number107589
JournalJournal of Diabetes and its Complications
Volume34
Issue number7
DOIs
StatePublished - Jul 2020

Keywords

  • Coupling
  • Disposition Index
  • Insulin secretion
  • Insulin sensitivity
  • Linearization
  • Slope

ASJC Scopus subject areas

  • Internal Medicine
  • Endocrinology, Diabetes and Metabolism
  • Endocrinology

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