Background 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, and clearly have prognostic relevance, in some cases predicting response to specific therapies.1,2 A complete phenotype of a given patients' 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 tests.3 Repeated testing is often unnecessary and expensive, but it is unclear to what extent this is a problem in RA.
Objectives We sought to determine how often serology is repeated in an RA cohort. In those that had serology repeated, we sought to determine how many times they had been tested, and for RF, how often the result changed.
Methods 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; only clear positives and negatives were included. To determine how often patients with positive index RF were retested, we examined those separately.
Results 100 patients were included. 73 (73%) had RF tested more than once. 29 (29%) had RF tested 4 times or more. 65 (65%) 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.
Conclusions Inappropriate repeat testing of RF is common, and the results only rarely change. Patients who have clearly tested positive for RF or anti-CCP should not be retested routinely. This study does not change the merits of repeat testing in equivocal cases.4 There is evidence that automated alerts from the laboratory identifying repeat testing can reduce this burden on laboratory services.3 It is likely that a great deal of repeat testing has been ordered by primary care physicians and it may therefore be worthwhile educating physicians that RF and anti-CCP have no role in assessing disease activity.
Gardette A, et al. High anti-CCP antibody titres predict good response to rituximab in patients with active rheumatoid arthritis. Joint Bone Spine. 2014;81(5):416-20.
Masi AT, et al. Prospective study of the early course of rheumatoid arthritis in young adults: comparison of patients with and without rheumatoid factor positivity at entry and identification of variables correlating with outcome. Semin Arthritis Rheum. 1976;4(4):299.
Niès J1, et al. Effects of automated alerts on unnecessarily repeated serology tests in a cardiovascular surgery department: a time series analysis. BMC Health Serv Res. 2010 Mar 19;10:70. doi: 10.1186/1472-6963-10-70.
Wiik AS1, et al. IUIS/WHO/AF/CDC Committee for the Standardization of Autoantibodies in Rheumatic and Related Diseases. Cutting edge diagnostics in rheumatology: the role of patients, clinicians, and laboratory scientists in optimizing the use of autoimmune serology. Arthritis Rheum. 2004 Apr 15;51(2):291-8.
Disclosure of Interest None declared