Proficiency testing (PT), also called external quality assessment, is an essential tool for quality assurance of the analytical testing process. PT has been used for decades to assist individual laboratories in determining that their measurement results conform to requirements for making medical decisions based on those results. In addition, when commutable samples are used, the mean or median results for different measurement procedures can be used to determine whether different measurement procedures produce results that agree well enough that the same medical decision will be made irrespective of the laboratory or measurement procedure used (1, 2).
PT samples are intended to mimic patient samples and thus to provide information that relates to medical decisions for patient samples. There is consensus that PT using commutable samples reflects the performance for patient samples, and that when noncommutable samples are used there may be artifacts that typically limit assessment of an individual laboratory's result to comparison to a peer group of similar measurement procedures and prevent using the mean or median results from different measurement procedures to assess agreement among results for patient samples (3).
In this issue of Clinical Chemistry , Stavelin et al. (4) demonstrate that different performance by different reagent lots or batches represented in a PT event can lead to erroneous decisions regarding the performance of individual laboratories or of measurement procedures. Furthermore, reagent lot–specific effects can influence interpretation when commutable or noncommutable samples are used. The Stavelin et al. report was based on point-of-care devices for which each reagent lot was calibrated by the manufacturer. However, the observations are generalizable to measurement procedures that use separate reagents and calibrators.
Consider the situation when commutable PT samples are used. The target …
[1]
J. Praestgaard,et al.
The accuracy of laboratory measurements in clinical chemistry: a study of 11 routine chemistry analytes in the College of American Pathologists Chemistry Survey with fresh frozen serum, definitive methods, and reference methods.
,
1998,
Archives of pathology & laboratory medicine.
[2]
W Greg Miller,et al.
Why commutability matters.
,
2006,
Clinical chemistry.
[3]
Cas Weykamp,et al.
Proficiency testing/external quality assessment: current challenges and future directions.
,
2011,
Clinical chemistry.
[4]
W Greg Miller,et al.
Commutability still matters.
,
2013,
Clinical chemistry.
[5]
Sverre Sandberg,et al.
The Importance of Reagent Lot Registration in External Quality Assurance/Proficiency Testing Schemes.
,
2016,
Clinical chemistry.
[6]
W. Miller,et al.
College of American Pathologists Conference XXIII on matrix effects and accuracy assessment in clinical chemistry: introduction.
,
1993,
Archives of pathology & laboratory medicine.
[7]
W Greg Miller,et al.
Commutability limitations influence quality control results with different reagent lots.
,
2011,
Clinical chemistry.