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Stability of insulin and C‐peptide measurement with long‐term frozen storage of serum: Implications for diabetes research studies
Author(s) -
Retnakaran Ravi,
Ye Chang,
Kramer Caroline K.
Publication year - 2019
Publication title -
diabetes, obesity and metabolism
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.445
H-Index - 128
eISSN - 1463-1326
pISSN - 1462-8902
DOI - 10.1111/dom.13617
Subject(s) - concordance , insulin , analyte , reproducibility , diabetes mellitus , c peptide , peptide , concordance correlation coefficient , confidence interval , medicine , chemistry , endocrinology , chromatography , biochemistry , mathematics , statistics
The current era of large‐scale clinical trials in diabetes has generated thousands of biological samples from study participants that are being stored long‐term under frozen conditions for the future measurement of analytes of interest. Insulin and C‐peptide are two such analytes that can provide insight into underlying pathophysiological processes (insulin sensitivity and β‐cell function). However, the validity of the inferences that may be drawn from such future measurements is contingent on the stability of these analytes after long‐term frozen storage. We conducted the present study to determine the stability of insulin and C‐peptide concentrations that were first measured on fresh serum at the time of collection, followed by frozen storage at –80°C for >5 years and then repeat measurement. Bland–Altman analyses revealed good agreement between the repeated insulin measurements and between the repeated C‐peptide measurements. The concordance correlation coefficient (CCC) confirmed reproducibility for both insulin (CCC 0.98, 95% confidence interval [CI] 0.96‐0.99) and C‐peptide (CCC 0.91, 95% CI 0.84‐0.95); thus, insulin and C‐peptide measurements are both stable and reproducible after long‐term frozen storage of serum samples.