MATERIALSAND METHODS
Testing procedures
When an agglutination test is requested by the
clinician a sheep cell agglutinationslidetest is first
performed (Rheumaton
111 ,
Wampole Lab., New
Jersey, USA).
If
this screening test is judged
positive the sample is further titrated in a microtiter
versionofthe Rose-Waalertest (RAPA
111 ,
Fujirebio.
Inc., Japan.) and a titer of
~1:40
is considered
positive. When determination of individual RF
classes is requested all samples are first screenedby
a sensitive EUSA system which detects the light
chains ofsolidphaseboundRF antibodies regardless
oftheir dass [24]. Samples positive in this screening
test (90% cut-off) are measured further in a similar
manner for elevation (95%cut-off) ofthe I
gM,
IgG
and IgA RF classes [17, 21] .
Clinical material
Every year between 7.000- 8.000 samples are sent
to the laboratory for determination of various
autoantibodies, compliment components, immune
complexes, IgE and other immunologkal para–
meters that are considered to be elinieally useful.
Out of 14.850 samples tested in 1991 and 1992 RF
was measured in 6.788 (46%). Both agglutination
Table
I.
andEUSAwas requested in 4.074 instances (60%)
and the RF findings in thesesamples are compared
in this paper.
RESULTS
Of the 6.788 samples tested for elevation of RF
in 1991 and 1992, 4.074 (60%) were tested bothby
EUSA and agglutination, 2.151 (32%) only by
agglutination and 563 (8%) only by EUSA. Table
I summarizes the results. Out of a total of 6.225
clinical samples tested by agglutination 515 (8%)
hada titer
of~1:40.
Of 4.637 samples tested by the
ELISAscreening test 456 (lO%) turned out to have
elevation of one or more RF classes.
In general there was a good rorrelation between
results of the agglutination and EUSA tests (Table
II). Thus, of the 4.074 samples tested by both
methods only 145 (3.6%) samples were discordant;
55
were positive by agglutination but negative by
ELISAand 90were positivebyEUSAbut negative
by agglutination. Over 80% of the agglutination
positive/ELISA negative samples had a titer of
l :40, i.e. the lowest titer considered positive. Table
III shows that of the90samples judged negative by
agglutination but positive by ELISA 76 (84%) had
RF tests performed at the Department of Immunology, Landspitalinn, Reykjavik in 1991 and 1992.
I.
AGGLUTINATION TESTS :
6.225 samples screened by agglutination (Rheumaton
111 )'
1.280 (21%) were Rheumaton positive
515 (8%) had a RAPA
111
titer
~
1:40
II. ELISA :
4.637 samples screened by ELISA '
689 (15%) were ELISA positive
456 (10%) had one or more RF classes elevated
' 4.074 of thesesamples were tested both by the ELISA and agglutination techniques.
Klinisk kemi
i
Norden 4, 1994
125
