Background and objectives Despite the well-established value of currently used diagnostic criteria for RA there is a constant demand for novel biomarkers to further improve early diagnosis notably in ACPA-negative patients. Inteleukin7 (IL-7) has been reported as a candidate diagnostic biomarker based on ACR-1987 criteria for RA, within 6 months of symptom development.1 The aim of the present study was to validate these results using EULAR-2010 criteria.
Materials and methods 255 patients attending early arthritis clinic were recruited. Demographic (age, gender, symptom duration) and clinical data (joint counts swollen and tender (SJC, TJC), CRP, DAS28, autoantibodies (RF and ACPA), SE) were collected. A commercial ELISA (R&D Systems, Abingdon, UK) was used to measure IL-7. Univariate and regression analysis were used to model outcome.
Results At follow-up over 24 months, 118 patients had a confirmed diagnosis of RA (EULAR-2010) while 137 were classified as non-RA (persistent UA, other diagnostic or non-inflammatory). The RA diagnosis was associated with ACPA, RF and SE positivity (p < 0.001, univariate). RA patients had significantly higher SJC, TJC, DAS28 (all p < 0.001) and CRP (p = 0.024). IL-7 tended to be lower in RA compared to non-RA (p = 0.100). To model for covariance, we used a regression analysis including IL7, ACPA (accounting for RF and SE as strongly associated), and SJC, TJC, CRP (as component of disease activity) including 227 patients with complete data set. IL-7 was the third best predictive marker (p = 0.035) following ACPA (p < 0.001) and SJC (p = 0.007). A second model was developed investigating ACPA-negative patients only (n = 147, complete data). IL7 was the second best predictive marker (p = 0.075) behind SJC (p = 0.013).
Conclusions This study validates previous results using the EULAR-2010 criteria for diagnosing RA (in UK population of patients), however the predictability associated with lower IL-7 is less significant than in the initial study using ACR-1987 criteria (in French cohort). IL-7 remains a potential biomarker for ACPA-negative RA although further validation with larger number of ACPA-negative RA is needed. Further replication studies are required to translate these results into clinical applicability.
Goëb VP, Aegerter R, Parmar P, et al. Progression to rheumatoid arthritis in early inflammatory arthritis is associated with low IL-7 serum levels. Ann Rheum Dis. 2013;72:1032–6