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Toward Standardization of Insulin Immunoassays

¹ Department of Pathology, Virginia Commonwealth University, Richmond, VA; ² Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Gent University, Gent, Belgium; ³ The Regional Endocrine Laboratory, University Hospital Birmingham, University of Birmingham, Birmingham, UK; ⁴ Mercodia, Uppsala, Sweden; ⁵ Nilsson Measurement Quality, Uppsala, Sweden; ⁶ Department of Laboratory Medicine and Pathology, Medical School, University of Minnesota, Minneapolis, MN.

^aAddress correspondence to this author at: PO Box 980286, Richmond, VA, 23298-0286. E-mail gmiller{at}vcu.edu.

Background: Measurement of circulating insulin may improve the classification and management of diabetes mellitus and assist in treating people with insulin resistance.

Methods: A work group convened by the American Diabetes Association evaluated results for a panel of 39 single donor sera measured by 10 commercial insulin methods from 9 manufacturers against an isotope dilution–liquid chromatography/tandem mass spectrometry (IDMS) measurement procedure calibrated using purified recombinant insulin. We used a candidate primary (pure substance) reference material, pooled serum, and single donor sera to evaluate approaches to achieve improved agreement of results between the routine and reference measurement procedures.

Results: Four of 10 methods had 95% of individual serum results within 32% of the IDMS concentrations. However, the bias vs IDMS was more than 15.5% for 7 of 10 methods in 36%–100% of individual samples. A purified recombinant insulin preparation used as a common calibrator did not improve harmonization of results among routine methods but was not used as instructed by all participants. Calibration using serum pools achieved bias <15.5% for nearly all results in the concentration range covered by the pools (>60 pmol/L). Calibration using a panel of individual sera was the most effective to improve harmonization of results over the full measuring range.

Conclusions: Agreement among methods can be improved by establishing traceability to the IDMS procedure using a panel of native sera. Pooled sera may be useful as trueness control materials. The usefulness of the pure insulin primary reference material [candidate reference material for insulin (cRMI)] requires clarification of protocols used by manufacturers.

The following articles in journals at HighWire Press have cited this article:

				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]