Clinical Research Papers:
OGTT 1h serum C-peptide to plasma glucose concentration ratio is more related to beta cell function and diabetes mellitus
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Hongmei Zhang1,*, Bingxian Bian2,*, Fan Hu1 and Qing Su1
1 Department of Endocrinology, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
2 Department of Clinical Laboratory, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
* These authors have contributed equally to this work
Qing Su, email:
Keywords: oral glucose tolerance test, C-peptide index, disposition index, β-cell function, diabetes mellitus
Received: December 21, 2016 Accepted: January 27, 2017 Published: February 09, 2017
Objective To clarify the association between C-peptide index and pancreatic beta cell function and diabetes.
Materials and methods We carried out a retrospective analysis of 1021 patients aged 27 to 80 without diabetes from January 2012 to January 2016. All subjects underwent a 75-g oral glucose tolerance test. Blood samples were drawn at 0, 30, 60, 120 and 180 min after the glucose load. Plasma glucose concentrations, serum insulin levels, C-peptide levels, hemoglobin A1c (HbA1c), and other biochemical indicators were determined. C-peptide index was calculated as the ratio of C-peptide to plasma glucose. Disposition index was calculated as the result of the insulin sensitivity × insulin secretion. Area under the receiver operating characteristic curve was used to compare the diagnostic ability of C-peptide index for type 2 diabetes.
Results C-peptide index 1h was the most related one to disposition index (r = 647, p<0.001) and C-peptide release (r = 0.879, p<0.001). Both C-peptide index 1h (Exp(β) = 0.28, p<0.001) and 2h (Exp(β) = 0.42, p<0.001) were independently associated with disposition index, but the OR of C-peptide index 1h for diabetes was much lower. Area under the receiver operating characteristic curve of both C-peptide index 1h and 2h were all above 0.9, but the area of C-peptide index 1h was the highest one (0.937 vs 0.917). C-peptide index 1h has the highest diagnostic value (sensitivity = 90%, specificy = 85.2% vs sensitivity = 83.5%, specificy = 87.9%).
Conclusion C-peptide index after oral glucose ingestion may reflect the maximal β-cell function and is more related to diabetes. C-peptide index 1h is the most relevant one.
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