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Automation and Analytical Techniques |
1 Department of Clinical Biochemistry and 2
The Regional Endocrine Laboratory, University Hospital Birmingham NHS Foundation Trust, University of Birmingham, Birmingham, United Kingdom.
3 Oxford Centre for Diabetes, Endocrinology & Metabolism, University of Oxford, Oxford, United Kingdom.
4 Diabetes Research Unit, Cardiff University, Cardiff, United Kingdom.
aAddress correspondence to this author at: Clinical Biochemistry, University Hospital Birmingham NHS Foundation Trust, Selly Oak Hospital, Raddlebarn Road, Birmingham B29 6JD, United Kingdom. Fax 44-121-414-0078; e-mail susan.manley{at}uhb.nhs.uk.
Background: The American Diabetes Association task force on standardization of insulin assays in 1996 showed wide variation in assay bias. Newer assays are specific for insulin, with several now available on automated immunoassay analyzers.
Methods: In 2004, we compared 11 commercially available insulin assays by analyzing 150 serum samples (99 fasting/51 postprandial) from study participants with various degrees of glucose intolerance (exclusions being type 1 diabetes, insulin treatment, or presence of insulin antibodies). All assays were calibrated against International Reference Preparation 66/304. One assay was not specific for insulin and another was an RIA; 10 assays used enzyme/chemiluminescent labels. Bland–Altman difference plots were modified to use the mean insulin from all assays on the x-axis as a common comparator.
Results: As in the 1996 study, insulin values from the different assays varied by a factor of 2, with the nonspecific assay ranking in the middle of the distribution. Spearman rank correlation coefficients, for ranking samples vs the mean, were 0.983–0.997. Both offsets and concentration-dependent differences were seen in the modified difference plots. Imprecision (mean CV) for automated assays (3%) was not significantly different from manual assays (5%). Similar values were obtained when one automated assay was run in laboratories in both the UK and the US. Results of 1 assay showed lower insulin concentrations in heparinized plasma than in serum.
Conclusions: Assay performance must be considered before comparing insulin results. The 2-fold variation in insulin results may be related to specificity, manufacturers’ calibration procedures or conversion factors.
The following articles in journals at HighWire Press have cited this article:
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  F. Magkos, B S. Mohammed, and B. Mittendorfer Enhanced insulin sensitivity after acute exercise is not associated with changes in high-molecular weight adiponectin concentration in plasma Eur. J. Endocrinol., January 1, 2010; 162(1): 61 - 66. [Abstract] [Full Text] [PDF]
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 M. A. Staten, M. P. Stern, W. G. Miller, M. W. Steffes, S. E. Campbell, and for the Insulin Standardization Workgroup Insulin Assay Standardization: Leading to measures of insulin sensitivity and secretion for practical clinical care Diabetes Care, January 1, 2010; 33(1): 205 - 206. [Full Text] [PDF]
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 W. G. Miller, L. M. Thienpont, K. Van Uytfanghe, P. M. Clark, P. Lindstedt, G. Nilsson, M. W. Steffes, and for the Insulin Standardization Work Group Toward Standardization of Insulin Immunoassays Clin. Chem., May 1, 2009; 55(5): 1011 - 1018. [Abstract] [Full Text] [PDF]
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P. E.M. De Pauw, I. Vermeulen, O. C. Ubani, I. Truyen, E. M.F. Vekens, F. T. van Genderen, J. W. De Grijse, D. G. Pipeleers, C. Van Schravendijk, and F. K. Gorus Simultaneous Measurement of Plasma Concentrations of Proinsulin and C-Peptide and Their Ratio with a Trefoil-Type Time-Resolved Fluorescence Immunoassay Clin. Chem., December 1, 2008; 54(12): 1990 - 1998. [Abstract] [Full Text] [PDF]
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S. E. Manley, S. D. Luzio, I. M. Stratton, T. M. Wallace, and P. M.S. Clark Preanalytical, Analytical, and Computational Factors Affect Homeostasis Model Assessment Estimates Diabetes Care, September 1, 2008; 31(9): 1877 - 1883. [Abstract] [Full Text] [PDF]
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D. Rodriguez-Cabaleiro, K. Van Uytfanghe, V. Stove, T. Fiers, and L. M. Thienpont Pilot Study for the Standardization of Insulin Immunoassays with Isotope Dilution Liquid Chromatography/Tandem Mass Spectrometry Clin. Chem., August 1, 2007; 53(8): 1462 - 1469. [Abstract] [Full Text] [PDF]
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R. Sapin Insulin Immunoassays: Fast Approaching 50 Years of Existence and Still Calling for Standardization Clin. Chem., May 1, 2007; 53(5): 810 - 812. [Full Text] [PDF]
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