Longitudinal analysis of ANA in the Systemic Lupus International Collaborating Clinics (SLICC) Inception Cohort.

A perception derived from cross-sectional studies of small systemic lupus erythematosus (SLE) cohorts is that there is a marked discrepancy between antinuclear antibody (ANA) assays, which impacts on clinicians' approach to diagnosis and follow-up. We compared three ANA assays in a longitudinal analysis of a large international incident SLE cohort retested regularly and followed for 5 years. Demographic, clinical and serological data was from 805 SLE patients at enrolment, year 3 and 5. Two HEp-2 indirect immunofluorescence assays (IFA1, IFA2), an ANA ELISA, and SLE-related autoantibodies were performed in one laboratory. Frequencies of positivity, titres or absorbance units (AU), and IFA patterns were compared using McNemar, Wilcoxon and kappa statistics, respectively. At enrolment, ANA positivity (≥1:80) was 96.1% by IFA1 (median titre 1:1280 (IQR 1:640-1:5120)), 98.3% by IFA2 (1:2560 (IQR 1:640-1:5120)) and 96.6% by ELISA (176.3 AU (IQR 106.4 AU-203.5 AU)). At least one ANA assay was positive for 99.6% of patients at enrolment. At year 5, ANA positivity by IFAs (IFA1 95.2%; IFA2 98.9%) remained high, while there was a decrease in ELISA positivity (91.3%, p<0.001). Overall, there was >91% agreement in ANA positivity at all time points and ≥71% agreement in IFA patterns between IFA1 and IFA2. In recent-onset SLE, three ANA assays demonstrated commutability with a high proportion of positivity and titres or AU. However, over 5 years follow-up, there was modest variation in ANA assay performance. In clinical situations where the SLE diagnosis is being considered, a negative test by either the ELISA or HEp-2 IFA may require reflex testing.

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Competing interests: MYC has received consulting fees from Janssen and MitogenDx (less than US$10 000). AEC has received consulting fees from AstraZeneca, BristolMyersSquibb, and Glaxo Smith Kline (less than US$10 000 each). KCH has consulted for or collaborated on research projects with Janssen, Glaxo Smith Kline, Exagen Diagnostics, Eli Lilly, Merck Serono, Astra Zeneca and Neutrolis (less than US$10 000 each). CG has received consulting fees, speaking fees, and/or honoraria from AstraZeneca, Abbvie, Amgen, UCB, GlaxoSmithKline, Merck Serono and BMS (less than US$10 000 each) and grants from UCB. Grants from UCB were not to CG but to Sandwell and West Birmingham Hospitals NHS Trust. DDG received consulting fees, speaking fees, and/or honoraria from GlaxoSmithKline (less than $10 000). INB has received consulting fees, speaking fees and/or honoraria from Eli Lilly, UCB, Roche, Merck Serono, MedImmune (less than US$10 000 each) and grants from UCB, Genzyme Sanofi and GlaxoSmithKline. EMG has paid consultation with investment analysts Guidepoint Global Gerson Lerman Group.Dr. Kalunian has received grants from UCB, Human Genome Sciences/GlaxoSmithKline, Takeda, Ablynx, Bristol-Myers Squibb, Pfizer and Kyowa Hakko Kirin, and has received consulting fees from Exagen Diagnostics, Genentech, Eli Lilly, Bristol-Myers Squibb, and Anthera (less than US$10 000 each). MJF is Director of Mitogen Diagnostics Corporation (Calgary, AB Canada) and a consultant to Werfen International (Barcelona, Spain), Grifols (Barcelona, Spain), Janssen Pharmaceuticals of Johnson & Johnson and Alexion Canada (less than US$10 000 each). The remainder of the authors have no disclosures.