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11
| 4 | 2003
Klinisk Biokemi i Norden
negligible commutability problems when compared
to routine results on patient sera. This assumption is
supported by measurements on the similar material:
IMEP 17 Material 1 [8].
X is already used in specific EQA projects:
Validation of S-Creatininium results after applica-
tion of a zero-point calibrator (EQUALIS 2003) and
studies of the commutability of control sera, e.g.
lyophilised materials (DEKS 2004).
The certificate
The certificate accompanying X is drafted according
to legal necessities, demands in ISO guide 31[9], EN
ISO 12286 [10], and ‘the IVD directive’ [11]. The cer-
tificate presents the certified and indicative values
(Table I and Table II)
All NFKK board members have provided inputs to
the certificate and approved it.
Traceability of the values
Certified values
The certified values and the related expanded
uncertainties are traceable to SI via values assigned
to IMEP-17 Material 1 by reference measurement
procedures and international certified reference
materials [7;12], except gamma-Glutamyltransferase
which is traceable to SI via CAL[3].
Indicative values
By definition the indicative values have no uncer-
tainty or expanded uncertainty traceable to the high-
est metrological order. Some of the values are trace-
able to reference measurement procedures performed
on CAL (ALT, Bilirubin, CK, Phosphate, Protein). The
only part of the uncertainty known for these values
is the part relating to the transfer of values from CAL
to X. The uncertainties of the reference measurement
procedures are unknown, albeit expected to be small-
er than the ones experienced in routine laboratories.
These values are transferred as the mean of the ratio
between the laboratory mean of X (meanX) and CAL
(meanCAL) multiplied with the certified value of CAL
(certifiedCAL) (Equation 1).
Indicative values traceable to CAL =
(Equation 1)
For the rest of the indicative values (ALP, Amylase,
AST, HDL-cholesterol, LD, Pancreatic amylase and
Transferrin) the values and the indicated standard devi-
ation of the mean are traceable to the arithmetic mean
of all NORIP participants’ mean measurement values
using routine methodologies (Equation 2). For enzymes
an IFCC 37 °C compatible methodology is used.
Indicative values traceable to NORIP participants =
(Equation 2)
Results
The tables are reprints from the first version of the
certificate. The numbers may be subject to later
changes and should in no way be used as a substi-
tute for the values provided in the certificate.
The use of X
X is not a substitute for the calibrators supplied
by manufactures of in-vitro medical devices.
The
certified values
are intended for evaluation and
verification of the performance of routine clinical
measurement procedures or validation.
The indica-
tive values
are important, because routine results
can be made traceable to the common NORIP refer-
ence intervals for the Nordic countries, thus satisfy-
ing the need for traceable reference intervals.
Practical use of X
A practical suggestion to the use of X, is to:
• Measure the working calibrator (supplied by the
IVD-manufacturer) 6-10 times in parallel with
6-10 measurements on X. The high number of
replicates is necessary to reduce the uncertainty.
• If post calibration modifications (e.g. factors,
slope and intercept) are performed locally the
values should be recalculated to the origi-
nal values, to ensure full traceability to the
calibrator of the instrument. Calculate the
arithmetic mean values. Make the following
correction to the mean value of X:
,
where M
X
and M
Calibrator
are the mean values of X
and the calibrator respectively and Target
Calibrator
is the assigned value of the calibrator [13].
