Abstract
Limited data are available on test utilization and intraindividual changes in rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (anti-CCP) in Korean patients that visit local clinics and hospitals. We retrospectively reviewed longitudinally measured RF and anti-CCP data in Korean patients to investigate the utilization and changes in test results through a laboratory information system. During the 10-year study period, 256,259 specimens were tested for RF. Among them, 32,567 (12.7%) specimens from 31,110 Korean adults had simultaneously measured anti-CCP results. Among them, 1110 (3.6%) subjects had follow-up test results. Among 351 patients with initial positive RF results, 290 (82.6%) had no qualitative change in RF from positive to negative values during follow-up. About 3.8% (29/759) of patients with initial negative results experienced qualitative changes in RF that were positive on follow-up. Among 182 patients with an anti-CCP-positive result at initial measurement, 174 (95.6%) had no qualitative change in anti-CCP from positive to negative or equivocal results during follow-up. About 0.5% (5/928) of patients with initial negative values experienced qualitative changes in anti-CCP to positive values on follow-up. The agreement of qualitative results between RF and anti-CCP was 80.8% (95% confidence interval 78.4–83.1%) at initial measurement and 80.6% (95% confidence interval 79.0–82.1%) overall. The results of this study can help inform utilization of RF and anti-CCP testing for Korean patients visiting local clinics and hospitals.
Highlights
Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune joint disease that is pathologically heterogeneous [1]
There are no confirmed diagnostic criteria for RA, early diagnosis is important for improving patient outcomes, and the classification criteria proposed by the American College of Rheumatology/European League Against
Rheumatism (ACR/EULAR) include clinical and serological variables such as rheumatoid factor (RF) and antiCCP, which can aid in diagnosing RA [2]
Summary
Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune joint disease that is pathologically heterogeneous [1]. The ACR/EULAR criteria propose that, if RF assay results are only available qualitatively, a positive result should be scored as a lowpositive [4,6]. With this testing approach and based on local laboratory standards, values equal to or less than the upper limit of normal (ULN) for the respective laboratory are defined as “Negative for RF” and are assigned 0 points; values that are >1–3 times the ULN are defined as “Low-positive” and assigned 2 points, and values that are >3 times the ULN are defined as “High-positive” and are assigned 3 points, based on ACR/EULAR
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