Measurement of Rheumatoid Factor in the
Clinical Laboratory
-
THE ADVANTAGES OF CLASS SPECIFIC TESTS
Thorbjörn Jonsson
&
Helgi Valdimarsson, Department oflmmunology, National University Hospital,
Landspitalinn, iS-101 Reykjavik, leeland
INTRODUCTION
General considerations about rheumatoid factor
Rheumatoid factors (RF) are classically defined as
antiborlies directed against the Fe part of immuno–
globulin G (IgG) molecules [l]. Elevation of RF
can
be
found in most patients with rheumatoid
arthritis (RA), but also in some patients with other
rheumatic diseases, infections, lung and liver
diseases and even cancer [1-3]. RF can also be
found in a some apparent!y healthy individuals
[4, 5]. Raised levels of serum IgM, IgG, IgA and
even lgE RF have been described in patients with
RA [6-8]. Elevation of RF often preeectes the
clinical onset of RA and longitudinal studies have
shown that RF elevation and isotype patterns are
relatively stable [9-11].
Hitherto, most clinicallaboratories havemeasured
RF by agglutination techniques which do not
distinguish between different RF classes. High
titer ofRF, as measured by agglutination, has been
associated with poor prognosis in RA and the
development ofbone erosions [12-14]. However,
RApatients who are seranegativejudged by agglu–
tination may also develop an erosive disease and
some patients with high agglutination RF titer may
have a good prognosis. A test that is more disease
specific and informative about prognosis of RA
patients is therefore required. Several studies have
indicated that measurement of individual RF clas–
ses is clinically more useful than conventional
agglutination tests (reviewed in 15). Thus, eleva–
tion of IgA RF has been reported to indicate poor
prognosis in RA, such as the development of bone
erosions [6, 7,16] and extra-articularmanifestations
[17, 18] while high levels of IgG RF are found in
most RA patients with rheumatoid nodules and
124
vasculitis [19, 20].
lt has further been shown that most patients with
definite RA have elevation ofboth lgMRF and IgA
RF [21, 22] while most patients with milder forms
of polyarthritis and other rheumatic conditions
have elevation of only one RF dass, usually lgM
RF [21, 23].
Thus, there is increasing evidence indicating that
measurement of individual RF classes is elinieally
useful. This seems to apply both for the diagnostic
and prognostic evaluation ofpatients with arthritis.
Methods for measurement of RF
Methods for measuring RF can be divided into two
main categories; conventional agglutination oflgG
coated particles (Rose-Waaler, Latex, etc.) and
solid phase assays (radioimmunoassay, ELISA).
The agglutinaton tests preferentially detect
polymeric RF, especially IgM RF, and can not be
used to measure individual RF classes.
TheDepartment oflmmunology at Landspitalinn
in Reykjavik is the only laboratory in leeland that
has measured different RF classes by solid phase
assay (ELISA) . This assay has now been in routine
use in the laboratory, in paralell with conventional
agglutination tests, for almost ten years. The
demand for dass specific measurement of RF has
been steadily increasing and is currently 68% ofthe
total RF requests. This suggests that the elinidans
consicter this service useful.
In this paper RF results obtained by the solid
phase technique and conventional agglutination
are campared and discussed in relation to to their
clinical value.
Klinisk kemi i Norden 4, 1994
