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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

Editor-in-Chief: Plebani, Mario

Ed. by Gillery, Philippe / Lackner, Karl J. / Lippi, Giuseppe / Melichar, Bohuslav / Payne, Deborah A. / Schlattmann, Peter / Tate, Jillian R.

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IMPACT FACTOR 2016: 3.432

CiteScore 2016: 2.21

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1437-4331
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Volume 53, Issue 10 (Sep 2015)

Issues

Assessing quality on the Sigma scale from proficiency testing and external quality assessment surveys

James O. Westgard
  • Corresponding author
  • Department of Pathology and Laboratory Medicine, University of Wisconsin, Madison, WI, USA
  • Westgard QC, Inc., Madison, WI, USA
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Sten A. Westgard
Published Online: 2015-02-11 | DOI: https://doi.org/10.1515/cclm-2014-1241

Abstract

Background: There is a need to assess the quality being achieved for laboratory examinations that are being utilized to support evidence-based clinical guidelines. Application of Six Sigma concepts and metrics can provide an objective assessment of the current analytical quality of different examination procedures.

Methods: A “Sigma Proficiency Assessment Chart” can be constructed for data obtained from proficiency testing and external quality assessment surveys to evaluate the observed imprecision and bias of method subgroups and determine quality on the Sigma scale.

Results: Data for hemoglobin A1c (HbA1c) from a 2014 survey by the College of American Pathologists (CAP) demonstrates that approximately two-thirds of the examination subgroups provide only two-Sigma quality when evaluated against the CAP requirement of an allowable total error of 6.0%. The weighted averages were 1.46 Sigma for a survey sample with an assigned value of 6.49% Hb (average bias 2.31%, CV 2.87%), 1.45 Sigma at 6.97% Hb (average bias 2.29%, CV 2.81%), and 1.75 at 9.65% Hb (average bias 1.55%, CV 2.71%). Maximum biases for examination subgroups were 5.7%, 5.8%, and 4.1%, respectively.

Conclusions: Assessment of quality on the Sigma scale provides evidence of the analytical performance that is being achieved relative to requirements for intended use and should be useful for identifying and prioritizing improvements that are needed in the analytical quality of laboratory examinations. In spite of global and national standardization programs, bias is still a critical limitation of current HbA1c examination procedures.

Keywords: external quality assessment; proficiency testing; Sigma quality

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About the article

Corresponding author: James O. Westgard, Westgard QC, Inc., 7614 Gray Fox Trail, Madison, WI 53717, USA, Phone: +1 608 833 4718, E-mail: ; and Department of Pathology and Laboratory Medicine, University of Wisconsin, Madison, WI, USA


Received: 2014-12-15

Accepted: 2015-01-16

Published Online: 2015-02-11

Published in Print: 2015-09-01


Citation Information: Clinical Chemistry and Laboratory Medicine (CCLM), ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: https://doi.org/10.1515/cclm-2014-1241.

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