General Introduction
The results of measurements of the catalytic activity concen–
tration of enzyrnes used in clinical chemistry are method de–
pendent. Consequently, different methodologies yield not only
numerically different values but vary in their analytical
bias for different isoenzyrne composition of samples (example:
alkaline phosphatases, EC 3.1.3.1, lactate dehydrogenases, EC
1.1.1.27, and amylases, EC 3.2.1.1), activation of enzyrnes
and suppression of interfering enzyrne reactions (example:
creatine kinase, EC 2.7.3.2), measurement of preformed holo–
enzyrne or of all preformed and activated apoenzyrnes (examp–
les: aminotransferases, EC 2.6.1.1 and 2.6.1.2.)
This dependence of results on methods has long been recogni–
zed as a barrier to the optimal clinical use of enzyrne as–
says.
The present profusion of different enzyrne methods has led to
a bewildering variety of reference ranges for ene and the
same enzyrne and therefore to difficulties in the interpreta–
tion of results, a less efficient use of the literature of
clinical enzymology, and difficulties in external quality as–
sessment programrnes.
The problem has been alleviated to a large extent by the in–
troduction of agreed or recomrnended methods, at National and
International levels. These initiatives have demonstrated
both the acceptability and the effectiveness of recomrnended
methcds.
However, the user is faced with a choice of different recom-
mendations, although their differences in performance may, in
many cases, be clinically insignificant.
Furthermore, no clear guidance exists as to how far defined
methods may be modified in the interest of analytical conve-
nience
(e.
g.
in such aspects as relative sample and reagent
Klinisk kemi
i
Norden 2: supp/, 1990
Il
