Jump to ContentJump to Main Navigation
Show Summary Details
More options …

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.

12 Issues per year

IMPACT FACTOR 2016: 3.432

CiteScore 2016: 2.21

SCImago Journal Rank (SJR) 2016: 1.000
Source Normalized Impact per Paper (SNIP) 2016: 1.112

See all formats and pricing
More options …
Volume 53, Issue 10


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


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


  • 1.

    Plebani M. The CCLM contribution to improvements in quality and patient safety. Clin Chem Lab Med 2013;51:39–46.Web of ScienceGoogle Scholar

  • 2.

    Westgard JO. Six Sigma quality design & control, 2nd ed. Madison WI: Westgard QC, Inc., 2006.Google Scholar

  • 3.

    Westgard JO. Basic method validation, 3rd ed. Madison WI: Westgard QC, Inc., 2008.Google Scholar

  • 4.

    Westgard JO. Basic QC practices, 3rd ed. Madison WI: Westgard QC, Inc., 2010.Google Scholar

  • 5.

    Westgard JO. Six Sigma risk analysis. Madison WI: Westgard QC, Inc., 2011.Google Scholar

  • 6.

    Westgard JO, Westgard SA. The quality of laboratory testing today: an assessment of sigma metrics for analytical quality using performance data from proficiency testing surveys and the CLIA criteria for acceptable performance. Am J Clin Pathol 2006;125:343–54.Google Scholar

  • 7.

    Westgard JO, Westgard SA. Basic quality management systems: essentials for quality management in the medical laboratory. Madison WI: Westgard QC, Inc., 2014:234–5.Google Scholar

  • 8.

    NGSP website. Available from: www.ngsp.org. Accessed 1 December, 2014.

  • 9.

    Bruns DE, Boyd JC. Few point-of-care hemoglobin A1c assay methods meet clinical needs. Clin Chem 2010;56:4–6.Google Scholar

  • 10.

    Thienpont LM, Van Utfanghe K, Cabaleiro DR. Metrological traceablity of calibration in the estimation and use of common medical decision-making criteria. Clin Chem Lab Med 2004;42:842–50.Google Scholar

  • 11.

    Magnusson B, Ellison SL. Treatment of uncorrected measurement bias in uncertainty estimation for chemical measurements. Anal Bioanal Chem 2008;390:201–13.Web of ScienceGoogle Scholar

  • 12.

    Woolworth A, Korpi-Steiner N, Miller JJ, Rao LV, Yundt-Pacheco J, Kuchipudi L, et al. Utilization of assay performance characteristics to estimate Hemoglobin A1c result reliability. Clin Chem 2014;60:1073–9.Web of ScienceGoogle Scholar

  • 13.

    Lenters-Westra E, Slingerland RJ. Three of 7 hemoglobin A1c point-of-care instruments do not meet generally accepted analytical performance criteria. Clin Chem 2014;60:1062–72.Google Scholar

  • 14.

    Jassam N, Yundt-Pacheco J, Jansen R, Thomas A, Barth JH. Can current analytical quality performance of UK clinical laboratories support evidence-based guidelines for diabetes and ischaemic heart disease? – A pilot study and a proposal. Clin Chem Lab Med 2013;51:1579–84.Google Scholar

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), Volume 53, Issue 10, Pages 1531–1535, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: https://doi.org/10.1515/cclm-2014-1241.

Export Citation

©2015 by De Gruyter. Copyright Clearance Center

Citing Articles

Here you can find all Crossref-listed publications in which this article is cited. If you would like to receive automatic email messages as soon as this article is cited in other publications, simply activate the “Citation Alert” on the top of this page.

Sten A. Westgard, Hassan Bayat, and James O. Westgard
Journal of Diabetes Science and Technology, 2017, Page 193229681772948
Rukiye Nar and Dilek Iren Emekli
Journal of Medical Biochemistry, 2017, Volume 0, Number 0
Hee Jin Huh, Yun Mi Park, Seungok Lee, Chunhwa Ihm, Soyeon Seo, Sang Gon Lee, Joonseok Park, and Hae-il Park
Annals of Laboratory Medicine, 2017, Volume 37, Number 4, Page 339
James O. Westgard and Sten A. Westgard
Clinics in Laboratory Medicine, 2017, Volume 37, Number 1, Page 85
James O. Westgard and Sten A. Westgard
Clinics in Laboratory Medicine, 2017, Volume 37, Number 1, Page 1
Sten A. Westgard
Clinical Biochemistry, 2016, Volume 49, Number 9, Page 699
James O. Westgard
Clinical Chemistry and Laboratory Medicine (CCLM), 2016, Volume 54, Number 2
Sten Westgard and Danijela Lucic
Clinical Microbiology Newsletter, 2015, Volume 37, Number 13, Page 103

Comments (0)

Please log in or register to comment.
Log in