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Open Access Original investigation

20/(fasting C-peptide × fasting plasma glucose) is a simple and effective index of insulin resistance in patients with type 2 diabetes mellitus: a preliminary report

Tsuyoshi Ohkura1*, Hideki Shiochi1, Youhei Fujioka1, Keisuke Sumi1, Naoya Yamamoto1, Kazuhiko Matsuzawa2, Shoichiro Izawa1, Hiroshi Kinoshita1, Hiroko Ohkura2, Masahiko Kato1, Shin-ichi Taniguchi2 and Kazuhiro Yamamoto1

Author Affiliations

1 Division of Cardiovascular Medicine, Endocrinology and Metabolism, Department of Molecular Medicine and Therapeutics, Tottori University Faculty of Medicine, Yonago, Tottori, Japan

2 Department of Regional Medicine, Tottori University Faculty of Medicine, Yonago, Tottori, Japan

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Cardiovascular Diabetology 2013, 12:21  doi:10.1186/1475-2840-12-21

Published: 22 January 2013

Abstract

Background

We developed a simple and new insulin resistance index derived from a glucose clamp and a meal tolerance test (MTT) in Japanese patients with type 2 diabetes mellitus.

Methods

Fifteen patients [mean age: 53 years, fasting plasma glucose (FPG) 7.7 mmol/L, HbA1c 7.1% (54 mmol/mol), body mass index 26.8 kg/m2] underwent a MTT and a glucose clamp. Participants were given a test meal (450 kcal). Plasma glucose and insulin were measured at 0 (fasting), 30, 60, 120, and 180 min. Serum C-peptide immunoreactivity (CPR) was measured at 0 (fasting; F-CPR) and 120 min. Homeostasis model assessment of insulin resistance (HOMA-IR) and insulin sensitivity indices (ISI) were calculated from the MTT results. The glucose infusion rate (GIR) was measured during hyperinsulinemic–euglycemic glucose clamps.

Results

The mean GIR in all patients was 5.8 mg·kg–1·min–1. The index 20/(F-CPR × FPG) was correlated strongly with GIR (r = 0.83, P < 0.0005). HOMA-IR (r = −0.74, P < 0.005) and ISI (r = 0.66, P < 0.01) were also correlated with GIR. In 10 patients with mild insulin resistance (GIR 5.0–10.0 mg·kg–1·min–1), 20/(F-CPR × FPG) was very strongly correlated with GIR (r = 0.90, P < 0.0005), but not with HOMA-IR and ISI (r = −0.49, P = 0.15; r = 0.20, P = 0.56, respectively). In patients with mild insulin resistance, plasma adiponectin (r = 0.65, P < 0.05), but not BMI or waist circumstance, was correlated with GIR.

Conclusions

20/(F-CPR × FPG) is a simple and effective index of insulin resistance, and performs better than HOMA-IR and ISI in Japanese patients with type 2 diabetes mellitus. Our results suggest that 20/(F-CPR × FPG) is a more effective index than HOMA-IR in Japanese patients with mild insulin resistance.

Keywords:
Glucose clamp; Meal tolerance test; Japanese patients; Insulin resistance; C-peptide; Type 2 diabetes mellitus