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Between-Lot Variation in External Quality Assessment of Glucose: Clinical Importance and Effect on Participant Performance Evaluation

¹ NOKLUS, Norwegian Quality Improvement of Primary Care Laboratories, Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway.

^aAddress correspondence to this author at: NOKLUS, Norwegian Quality Improvement of Primary Care Laboratories, Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, UNIFOB AS, Boks 6165 Postterminalen, 5892 Bergen, Norway. Fax 47-55586710; e-mail gunn.kristensen{at}isf.uib.no.

Background: External quality assessment schemes (EQAS) are conducted to evaluate user performance (participant assessment) and to assess different methods and instruments (method assessment). The quality of control materials is crucial to achieving these goals. Inconsistencies in between-lot variations detected by use of different control and sample materials may affect EQAS outcomes.

Methods: For the Accu-Chek Sensor, Precision Xtra, Ascensia Elite, and HemoCue 201 glucometers, 3 different lots of glucose strips were used with each instrument. Method assessment results from analysis of capillary blood and 3 control materials were used to calculate between-lot differences. A simulation study was performed to evaluate the effect of between-lot variation on participant assessment results.

Results: With the Precision Xtra, the results obtained with EQA control material mirrored those obtained with capillary blood, but for the other instruments, we found between-lot differences of as much as 1.3 mmol/L, which were substantially greater than those found with capillary blood and of clinical importance at decision limits. The simulation study showed an effect on participant assessment results related to the target values, with the percentage of poor results decreasing (38%, 10%, and 4%) with the use of common, method-specific, and lot-specific target values, respectively.

Conclusions: Between-lot variation may influence participant EQA results for participant and method assessments. The clinical relevance of between-lot variation discovered in EQAS using noncommutable control materials should be examined by use of native blood samples.

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				K. Dungan, J. Chapman, S. S. Braithwaite, and J. Buse Glucose Measurement: Confounding Issues in Setting Targets for Inpatient Management Diabetes Care, February 1, 2007; 30(2): 403 - 409. [Full Text] [PDF]

				G. B.B. Kristensen, K. Nerhus, G. Thue, and S. Sandberg Results and Feasibility of an External Quality Assessment Scheme for Self-Monitoring of Blood Glucose Clin. Chem., July 1, 2006; 52(7): 1311 - 1317. [Abstract] [Full Text] [PDF]