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Divide and conquer
Back to Feature Story
March 2003
CLIA ’88 regulations use the term "calibration verification" to refer
to the verification of correct method calibration and validation of
the AMR. The CAP’s checklists use separate terms, as follows, to identify
two distinct processes required for good laboratory practice.
Analytical measurement range validation:
The process of confirming that the assay system will correctly recover
the concentration or activity of the analyte over the AMR. The materials
used for validation must be known to have matrix characteristics
appropriate for the method. The matrix of the sample-that is, the
environment in which the sample is suspended or dissolved-may influence
the measurement of the analyte. In many cases, the method manufacturer
will recommend suitable materials. The test specimens must have
analyte values that, at a minimum, are near the low, midpoint, and
high values of the AMR. Specimen target values can be established
by comparison with peer group values for reference materials, by
assignment of reference or comparative method values, and by dilution
or admixture ratios of one or more specimens with known values.
Each laboratory must define limits for accepting or rejecting validation
tests of the AMR. The AMR must be revalidated at least every six
months, at changes in major system components, and when a complete
change in reagents for a procedure is introduced, unless the lab
can demonstrate that changing reagent lot numbers does not affect
the range used to report patient/client test results. Routine reagent
lot changes may not require AMR revalidation if they occur within
the six-month interval. The laboratory director should determine
what constitutes a major system component change or a "complete"
change in reagents that would require revalidation of the AMR. Manufacturers’
instructions should be followed.
Calibration verification:
The process of confirming that the current calibration settings
remain valid for a method. If calibration verification confirms
that the current calibration settings are valid, it is not necessary
to perform a complete calibration or recalibration of the method.
Calibration verification can be accomplished in several ways. If
the method manufacturer provides a calibration validation or verification
process, it should be followed. Other techniques include (1) assay
of the current method calibration materials as unknown specimens
and determination that the correct target values are recovered,
and (2) assay of matrix-appropriate materials with accurate target
values that are specific for the method. Materials for calibration
verification must have a matrix appropriate for the clinical specimens
assayed by that method and target values appropriate for the measurement
system. In general, routine control materials are not suitable for
calibration verification, except in situations where the material
is specifically designated by the method manufacturer as suitable
for verification of the method’s calibration process.
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