Detection of anti-nuclear antibodies. Added-value of solid phase assay?
Agmon-Levin et al. formulated recommendations for the
assessment of anti-nuclear antibodies (ANA). Indirect immunofluorescence
(IIF) is considered the reference method for ANA screening, which is in
agreement with the ACR position statement. The recommendations are
based on current knowledge and expert experience.
However, as recognized by Meroni and Schur, no well-planned studies comparing the diagnostic accuracy of the old IIF and the new methods have been undertaken.
In a recent study, IIF was compared to a new automated method for connective disease screening [fluoroenzymeimmunoassay (FEIA) (EliA CTD screen, Thermo Fisher)] using samples obtained at the time of diagnosis from well characterized patients and controls. Diagnostic accuracy data [for systemic lupus erythematosus (SLE), systemic sclerosis (SSc) and Sjögren's syndrome (SS)] from this study is recapitulated in Table 1. For comparison, data from a multinational study on IIF is included in the Table as well. The results for IIF in the two studies were comparable, thereby validating the study population. A higher specificity was observed for FEIA than for IIF (especially at IIF cutoff dilution 1:80), whereas sensitivity was higher for IIF than for FEIA for SLE and SSc, but not for SS. The diagnostic performance of FEIA was comparable to the performance of a multiplexed bead assay. For the combination of IIF and FEIA the highest likelihood ratios (LR) (35 -50) were found for double positivity (FEIA and IIF), the lowest (0.03- 0.11) for double negativity. IIF positivity combined with FEIA negativity (22-25% of SLE and SSc patients) had a low LR (<5).
Using the area under the receiver operating characteristic curve (AUC), the diagnostic performance of four diagnostic strategies was compared; (i) IIF on all samples, (ii) FEIA on all samples, IIF on all samples and FEIA on IIF-positive samples, and (iv) both tests (IIF and FEIA) on all samples. The results are summarized in Figure 1. For SLE, the best strategy was performing both tests on all samples. The second best strategy (p=0.08 for IIF cutoff dilution 1:80; p=0.03 for IIF cutoff dilution 1:160) was screening with IIF and FEIA on IIF-positive samples. The AUC of these strategies was significantly higher than the AUC of only IIF or only FEIA. For SSc, screening with IIF and performing FEIA on IIF-positive samples was comparable to IIF and FEIA on all samples. The AUC of these strategies was significantly higher than the AUC of only IIF or only FEIA. For SS, the best strategy was performing both tests on all samples. The AUC of this strategy was not significantly higher than the AUC of only FEIA, but was significantly higher than the AUC of screening with IIF and FEIA on IIF-positive samples.
Taken together, our results show that favorable strategies are disease-dependent and that combining IIF with solid phase assay can increase the diagnostic information (e.g. refined estimation of LR for disease).
For the additional Table and Figure see the Electronic Pages of the coming issues.
1. Agmon-Levin N, Damoiseaux J, Kallenberg C, et al. International recommendations for the assessment of autoantibodies to cellular antigens referred to as anti-nuclear antibodies. Ann Rheum Dis 2013 Oct 14. doi: 10.1136/annrheumdis-2013-203863. [Epub ahead of print]
2. Meroni PL, Schur PH. ANA screening: an old test with new recommendations. Ann Rheum Dis 2010;69:1420-2.
3. Op De Beeck K, Vermeersch P, Verschueren P, et al. Detection of antinuclear antibodies by indirect immunofluorescence and by solid phase assay. Autoimmun Rev 2011;10:801-8.
4. Tan EM, Feltkamp TE, Smolen JS, et al. Range of antinuclear antibodies in "healthy" individuals. Arthritis Rheum 1997;40:1601-11.
5. Op De Be?ck K, Vermeersch P, Verschueren P, et al. Antinuclear antibody detection by automated multiplex immunoassay in untreated patients at the time of diagnosis. Autoimmun Rev 2012;12:137-43.
Conflict of Interest:
XB has received a lecture fee from Thermo Fisher