Abstract
Objectives: A perception derived from cross-sectional studies of small SLE cohorts is that there is a marked discrepancy between antinuclear antibody (ANA) assays, which impacts on clinician’s 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 five years.
Methods: 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 enzyme-linked immunosorbent assay (ELISA), and SLE-related autoantibodies were performed in one central laboratory. Frequencies of positivity, titres/units, and IFA patterns were compared using McNemar, Wilcoxon, and kappa statistics, respectively.
Results: 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 (176.3AU [IQR 106.4-203.5]). 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.
Conclusion: In recent-onset SLE, three ANA assays demonstrated commutability with a high proportion of positivity and titres/units. However, over five 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.
Methods: 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 enzyme-linked immunosorbent assay (ELISA), and SLE-related autoantibodies were performed in one central laboratory. Frequencies of positivity, titres/units, and IFA patterns were compared using McNemar, Wilcoxon, and kappa statistics, respectively.
Results: 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 (176.3AU [IQR 106.4-203.5]). 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.
Conclusion: In recent-onset SLE, three ANA assays demonstrated commutability with a high proportion of positivity and titres/units. However, over five 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.
Original language | English |
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Pages (from-to) | 1143-1150 |
Journal | Annals of the Rheumatic Diseases |
Volume | 81 |
Issue number | 8 |
Early online date | 25 Mar 2022 |
DOIs | |
Publication status | E-pub ahead of print - 25 Mar 2022 |
Keywords
- Antinuclear antibodies
- ELISA
- Systemic Lupus Erythematosus
- immunoassays
- longitudinal
- performance