Repeating Serology Testing in RA: Are We Adopting a Rational Approach?
Orr C, Young F, Veale DJ.
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre, University College Dublin, Ireland.
There is an absence of literature on the merits or problems of repeat serology testing in patients with RA. The auto-antibodies RF and anti-CCP have significance far outreaching assistance in diagnosis, clearly having prognostic relevance, and in some cases predicting response to specific therapies.(1,2) A complete phenotype of a patient’s disease is only clear when both these sets of antibodies are known. There are indications from other specialities that serology testing is often repeated in as much as 15% of the time.(3) Repeated testing is often unnecessary and expensive, but it is unclear to what extent this is a problem in RA.
To determine how often serology is repeated in an RA cohort and to determine how often repeat testing of RF yields a different result.
We analysed how many times each patient in a cohort comprising consecutive patients attending clinic in July 2014 had been tested for each auto-antibody. Equivocal results were excluded, leaving only clear positive and negative results. We examined separately how many times an initial positive RF was retested, and how often the first (index) RF result changed.
100 patients were included. 73 (73%) had RF tested more than once. 29 (29%) had RF tested 4 times or more. 64 (64%) were positive for RF at index testing. Of these patients, 50 (78.1%) had RF tested more than once and 22 (34.4%) had RF tested 4 times or more. 1 positive RF at index measured negative but positive again on third testing. 1 negative RF at index became positive at second testing. Anti-CCP status was known for 85 patients. 21 (24.7%) were tested more than once, and 4 (4.7%) were tested 4 times or more. 59 (69.4%) were positive for anti-CCP at index testing. Of these patients, 11 (18.6%) had anti-CCP tested more than once and 1 (1.7%) were tested 4 times or more.
Patients who have clearly tested positive for RF or anti-CCP should not be retested routinely but this study does not change the merits of repeat testing in equivocal cases. Inappropriate repeat testing of RF is common and the results only rarely change.(4) There is evidence that automated alerts from the laboratory identifying repeat test requests can reduce this burden on laboratory services(3), and educating the source of the requests (e.g. primary care physicians), regarding the utility of the test might also reduce the burden.