Klinisk Biokemi i Norden · 4 2014
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common is to use lyophilized control materials, esta-
blish peer group target values, use an acceptability
limit of 15% and distribute four samples per year.
Most of the countries organize educational activities
with focus on quality improvement. The study in
paper II demonstrates that most European countries
do not provide EQA schemes for POC INR methods,
and that the disadvantages in most of the provided
schemes were the use of non-commutable control
materials making comparison between different POC
methods impossible.
An important objective in EQA is to evaluate sys-
tematic deviations (bias) between methods. This is,
however, not possible when non-commutable control
materials with peer group target values are used. The
aim of paper III (3) was to develop a new EQA model
in which an evaluation of method bias was incor-
porated in EQA schemes that use non-commutable
materials. The model was developed based on the
concept that a selected group of primary care labo-
ratories should establish an estimate of the systema-
tic deviation of the POC method from a designated
comparison method by using fresh patient samples,
and this information should then be incorporated in
the feedback to the participants in the EQA scheme
using non-commutable control materials. As a con-
sequence, the participants will get more information
about the analytical quality of their method. The
model was applied twice in POC INR surveys among
1341 and 1578 participants, respectively. To estimate
bias for each POC INR method, about 100 native
patient samples were analyzed both by a selected
group of expert primary care laboratories (72 and
69 in the first and second survey, respectively) and
on a designated comparison method. Both method
bias and the deviation of a single-participant result
in the EQA schemes were evaluated against sepa-
rate analytical quality specifications. Two POC INR
methods (CoaguChek XS Plus and Simple Simon)
fulfilled the quality specification for bias, whereas
one did not (Thrombotrack). More than 90% of the
participants received results within the quality spe-
cification for a deviating EQA result. In conclusion,
a new EQA model for POC methods was proposed in
paper III. This model can be used in situations where
commutable control materials are not available. An
editorial in
Clinical Chemistry
has recommended
that EQA organizers should implement this proposed
EQA model (4).
References
1. Stavelin A, Petersen PH, Solvik U, Sandberg S.
Internal quality control of prothrombin time
in primary care: comparing the use of patient
split samples with lyophilized control materi-
als. Thromb Haemost 2009; 102:593-600.
2. Stavelin A, Meijer P, Kitchen D, Sandberg S.
External quality assessment of point-of-care
international normalized ratio (INR) testing
in Europe. Clin Chem Lab Med 2012; 50:81-8.
3. Stavelin A, Petersen PH, Solvik UO, Sandberg
S. External quality assessment of point-of-care
methods: Model for combined assessment of
method bias and single participant perfor-
mance by the use of native patient samples and
non-commutable control materials. Clin Chem
2013; 59:363-71.
4. Horowitz GL. Proficiency testing matters. Clin
Chem 2013; 59:335-37.
Rölleka (Achillea millefolium). Foto: Henrik Alfthan.
