for these differences, and these can be
summarised as follows:
• Companies: There are many IVD method
manufacturers around the world. Their individual
methods may have different specimen
requirements; employ different method designs
and use different signal detection systems.
Variability may also be introduced by local
modification to a company product
• Components: Methods may use different
calibrators; different enzymes and substrates;
different antigens and antibodies; and a variety
of other reagents
• Conditions: Different methods have variability
in reaction time; temperature, pH and often use
different software and curve fits to derive results
• Common target: Although methods will quote
figures for imprecision and accuracy (trueness)
these are of limited value unless they can be
related to a common, international reference
system.
Patients are
entitled to
believe that all
methods for the
same analyte
will give similar
results on a
single specimen.
Sadly, for many
analytes this
is not currently
the case
Traceability in laboratory medicine
Metrology is the science of measurement. The
application of metrology provides the key to
reducing measurement variability by facilitating
the adoption of international reference systems to
enable alignment from different methods. The
increasing application of metrological traceability
in laboratory medicine (TLM) to underpin those
reference systems is reducing the variables that
are responsible for methods giving different
results. 6 TLM is an important area of laboratory
science that is often poorly understood. Achieving
TLM is a global multi-stakeholder, cooperative
activity involving metrologists; international
standards organisations; scientific and clinical
experts from international professional bodies;
healthcare regulators; and the IVD industry. 7
Metrological traceability is defined as the
property of a measurement result, which can
be related to a reference standard through
a documented unbroken chain of calibrations.
The principles of a reference measurement system
for establishing metrological traceability are
described in the relevant International Standards
Organisation (ISO) document. 8 The components
of a reference measurement system comprise
reference materials (calibrators) and reference
measurement procedures (methods), both of
which exist at different hierarchical levels.
The inter-relationship between the components
of a reference measurement system may be
described in the metrological traceability chain. 8
Figure 1 depicts this traceability chain with
higher order reference materials and
measurement procedures at the top and lower
order towards the bottom. At the top of the chain
is the definition of the measurand, the substance
intended to be measured, expressed in SI units.
The hierarchy of reference materials and
measurement procedures is depicted by the rising
metrological traceability arrow. Descent through
the traceability chain is accompanied by
increasing measurement uncertainty as depicted
by the downward arrow. Figure 1 also depicts the
contributions to TLM of the metrology institute or
reference laboratory; the IVD method
manufacturer; and the routine service laboratory.
The relevance of TLM may be explained by
FIGURE 1
The metrological traceability chain
Definition of measurand: concentration in SI units
Primary reference material
Primary reference
measurement procedure
Secondary reference
measurement procedure
Secondary calibrator
Manufacturer master calibrator
Manufacturer standing
measurement procedure
IVD method
manufacturer
Product calibrator Manufacturer standing
measurement procedure
Patient result Routine laboratory method
Adapted from EN ISO 17511 2003 8
11
HHE 2019 | hospitalhealthcare.com
Routine lab
Metrology institute
/ Reference lab
Primary calibrator