settings, the personnel are typically trained in the
performance of the method but usually have only a
limited amount of training and experience in general
laboratory practices. Consequently, the method
needs to be easy to perform and highly reliable if it
is to be dependable. For home testing, in which the
patient or a family member performs the test, the
need for method ease and reliability is even greater.
Method safety encompasses the whole range of
safety considerations in the performance of a
method. It includes concerns for the biological,
chemical, and radiation hazards to which the labora-
tory staff may be exposed during the preparation of
samples and the performance of the method and for
the electrical and mechanical safety of equipment
used in the performance of the method. Safety
considerations may determine who can run the
method and where the method can be set up in the
laboratory.
METHOD EVALUATION
There are two kinds of method evaluations: the
evaluation of a newly developed method, which is
usually undertaken and reported by the laboratory
scientists who devised the method, and the evalua-
tion of a validated method, which is performed by
the laboratorians who are considering setting up the
method in their clinical laboratory. The first type
of evaluation is ordinarily conducted under the best
possible laboratory conditions and with the loving
attention of the developers. The second type of
evaluation, which is usually conducted under routine
laboratory conditions, establishes how well a method
performs in the laboratory in which it will be used.
The performance may not be as good as that
reported by the developers because of the differences
in the operating conditions. That is why on-site
method evaluation is necessary before implementing
any method. The evaluation of a newly developed
method must be very thorough. The report of the
evaluation should include the components listed in
Table 2.5.
Laboratory methods are developed for three
reasons. The first is to provide a method for the
measurement of an analyte which is recognized to be
clinically useful but for which there is no existing
method. The second is to provide a method with
analytic quality superior to that of other methods
currently in use and the third is to provide a method
of greater practicability than that of currently
available methods. In an exemplary evaluation of a
new method for determining plasma phosphate
concentration, Luque de Castro
et al.
(1995) indicate
that their primary motivation for developing the
method was to improve practicability. The method
uses a flow injection (FI) system with immobilized
enzymes. As they state, immobilized enzymes
have several advantages over the use of
dissolved enzymes in batch assays, such as
lower analytical cost, higher selectivity and
stability, and long life span.
A similar method had already been developed,
Male and Luong (16) developed the first FI
method for the determination of phosphate
with immobilized [nucleoside phosphorylase]
and xanthine oxidase
but that method used amperometric detection of the
reaction product. The method of Luque de Castro
et
al.
produces a different indicator product that is
detected fluorometrically.
Method description
The description of the method should include the
same items as are found in a written measurement
procedure (Table 2.3). The level of detail should
also be comparable to that of a written procedure:
using only the method description and general
laboratory knowledge, a reader should be able to
setup and perform the method in his or her clinical
laboratory.
Sampling and specimen handling.
The report
should state the kinds of specimens that can be
assayed using the method. It should be noted if
special processing is required of some specimens.
For example, urine may need to be diluted prior to
measurement. The kinds of specimens actually used
in the performance of the method evaluation should
be indicated.
Laboratory Methods
2-14
Table 2.5
Components of a Method Evaluation Report
1. Statement of the motivation for the development
of the method
2. Description of the method
3. Description of the optimization of analytical variables
4. Characterization of the calibration curve
5. Assessment of analytical quality
6. Determination of analytical range
