Analytical and clinical comparison of two fully automated immunoassay systems for the detection of autoantibodies to extractable nuclear antigens

Clinical Performance of Two Automated Immunoassays, EliA CTD Screen and QUANTA Flash CTD Screen Plus, for Antinuclear Antibody Screening

Background

Recently, two fully automated immunoassays for antinuclear antibody (ANA) screening were introduced EliA CTD Screen (Thermo Fisher Scientific, Freiburg, Germany) and QUANTA Flash CTD Screen Plus (Inova Diagnostics, San Diego, USA). We evaluated their clinical performance in comparison with the indirect immunofluorescence assay (IIFA) and analyzed samples with discrepant results.

Methods

In total, 406 serum samples (206 from patients undergoing routine checkups and 200 from rheumatology clinic patients) were assayed using EliA, QUANTA Flash, and IIFA. We evaluated assay concordance and agreement and confirmed the presence of anti-extractable nuclear antigen (ENA) antibodies in samples with discrepant automated immunoassay and IIFA results. Additionally, we compared the clinical performance of each assay in diagnosing ANA-associated rheumatic disease (AARD) and adjusted the cut-off values.

Results

In rheumatology clinic samples, the concordance and agreement were 91.5% and strong between EliA and QUANTA Flash, 79.0% and weak between EliA and IIFA, and 80.5% and moderate between QUANTA Flash and IIFA, respectively. In automated immunoassay-positive, IIFA-negative samples (N=15), all anti-ENA antibodies detected (6/15) were anti-Sjögren’s syndrome antigen A/Ro (Ro60) antibodies. The automated immunoassays and IIFA showed high accuracy for diagnosing AARD, and adjusted cut-off values improved their sensitivities (EliA with 0.56 ratio, 82.9% sensitivity; QUANTA Flash with 9.7 chemiluminescent units, 87.8% sensitivity).

Conclusions

The two automated immunoassays showed reliable performance compared with IIFA and can be efficiently used with the IIFA in clinical immunology laboratories. Clinical cut-off values can be adjusted according to the workflow in each laboratory.

Understanding and interpreting antinuclear antibody tests in systemic rheumatic diseases

Antinuclear antibodies (ANAs) are valuable laboratory markers to screen for and support the diagnosis of various rheumatic diseases (known as ANA-associated rheumatic diseases). The importance of ANA testing has been reinforced by the inclusion of ANA positivity as an entry criterion in the 2019 systemic lupus erythematosus classification criteria. In addition, specific ANAs (such as antibodies to Sm, double-stranded DNA (dsDNA), SSA/Ro60, U1RNP, topoisomerase I, centromere protein B (CENPB), RNA polymerase III and Jo1) are included in classification criteria for other rheumatic diseases. A number of techniques are available for detecting antibodies to a selection of clinically relevant antigens (such as indirect immunofluorescence and solid phase assays). In this Review, we discuss the advantages and limitations of these techniques, as well as the clinical relevance of the differences between the techniques, to provide guidance in understanding and interpreting ANA test results. Such understanding not only necessitates insight into the sensitivity and specificity of each assay, but also into the importance of the disease context and antibody level. We also highlight the value of titre-specific information (such as likelihood ratios).

A hierarchical bivariate meta-analysis of diagnostic test accuracy to provide direct comparisons of immunoassays vs. indirect immunofluorescence for initial screening of connective tissue diseases

OBJECTIVES

To compare indirect immunofluorescence (IIF) for antinuclear antibodies (ANA) against immunoassays (IAs) as an initial screening test for connective tissue diseases (CTDs).

METHODS

A systematic literature review identified cross-sectional or case-control studies reporting test accuracy data for IIF and enzyme-linked immunosorbent assays (ELISA), fluorescence enzyme immunoassay (FEIA), chemiluminescent immunoassay (CLIA) or multiplex immunoassay (MIA). The meta-analysis used hierarchical, bivariate, mixed-effect models with random-effects by test.

RESULTS

Direct comparisons of IIF with ELISA showed that both tests had good sensitivity (five studies, 2321 patients: ELISA: 90.3% [95% confidence interval (CI): 80.5%, 95.5%] vs. IIF at a cut-off of 1:80: 86.8% [95% CI: 81.8%, 90.6%]; p = 0.4) but low specificity, with considerable variance across assays (ELISA: 56.9% [95% CI: 40.9%, 71.5%] vs. IIF 1:80: 68.0% [95% CI: 39.5%, 87.4%]; p = 0.5). FEIA sensitivity was lower than IIF sensitivity (1:80: p = 0.005; 1:160: p = 0.051); however, FEIA specificity was higher (seven studies, n = 12,311, FEIA 93.6% [95% CI: 89.9%, 96.0%] vs. IIF 1:80 72.4% [95% CI: 62.2%, 80.7%]; p < 0.001; seven studies, n = 3251, FEIA 93.5% [95% CI: 91.1%, 95.3%] vs. IIF 1:160 81.1% [95% CI: 73.4%, 86.9%]; p < 0.0001). CLIA sensitivity was similar to IIF (1:80) with higher specificity (four studies, n = 1981: sensitivity 85.9% [95% CI: 64.7%, 95.3%]; p = 0.86; specificity 86.1% [95% CI: 78.3%, 91.4%]). More data are needed to make firm inferences for CLIA vs. IIF given the wide prediction region. There were too few studies for the meta-analysis of MIA vs. IIF (MIA sensitivity range 73.7%-86%; specificity 53%-91%).

CONCLUSIONS

FEIA and CLIA have good specificity compared to IIF. A positive FEIA or CLIA test is useful to support the diagnosis of a CTD. A negative IIF test is useful to exclude a CTD.

Detection of Anti-Extractable Nuclear Antigens in Patients with Systemic Rheumatic Disease via Fluorescence Enzyme Immunoassay and Its Clinical Utility

PURPOSE

Testing for autoantibodies to extractable nuclear antigens (ENAs) plays an important role in the diagnosis and management of systemic rheumatic disease. Currently, no gold standard tests are available for detecting anti-ENAs. To address this gap, we aimed to identify an assay that exhibits satisfactory diagnostic performance in the detection of five common anti-ENAs by comparing two commonly used assays, an automated fluorescent enzyme immunoassay (FEIA) and a microplate ELISA assay.

MATERIALS AND METHODS

Sera from 100 patients with systemic rheumatic disease were collected and assayed with FEIA and microplate ELISA to detect anti-ENAs. Statistical analyses were performed to check the agreement rate between the two platforms using kappa coefficients. Analytical sensitivity and specificity for each assay were calculated.

RESULTS

The concordance rates between ELISA and FEIA ranged from 89% for anti-RNP to 97% for anti-Scl-70, and the kappa coefficients of the two assays were in the range of 0.44 to 0.82. Between the two assays, a significant difference in sensitivity and specificity was seen only for anti-Sm and anti-RNP, respectively.

CONCLUSION

In this study, FEIA and ELISA showed comparable efficiency for detecting anti-ENAs.

ANA as an entry criterion for the classification of SLE

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease with highly variable clinical and immunological manifestations. In the classification of patients with this condition, the presence of an antinuclear antibody (ANA) is an important element, with new criteria from the American College of Rheumatology and European League against Rheumatism positioning ANA positivity by an immunofluorescence assay on HEp2-cells (HEp2-IFA) or by an equivalent solid phase assay as the entry criterion. This positioning is based on assumptions about the frequency of ANA positivity in SLE as well as the reliability of the assays. Studies indicate that these assumptions are still a matter of uncertainty since both types of assay show considerable variability and patients with SLE may display negative results in ANA testing. These findings suggest caution in positioning ANA positivity as an entry criterion for classification and point to the value of alternative serological approaches for ANA determinations.

Diagnostic laboratory tests for systemic autoimmune rheumatic diseases: unmet needs towards harmonization

Autoantibodies are helpful tools not only for the diagnosis and the classification of systemic autoimmune rheumatic diseases (SARD) but also for sub-grouping patients and/or for monitoring disease activity or specific tissue/organ damage. Consequently, the role of the diagnostic laboratory in the management of SARD is becoming more and more important. The advent of new techniques raised the need of updating and harmonizing our use/interpretation of the assays. We discuss in this opinion paper some of these issues. Indirect immunofluorescence (IIF) was originally suggested as the reference technique for anti-nuclear antibody (ANA) detection as previous solid phase assays (SPA) displayed lower sensitivity. The new available SPA are now offering better results and can represent alternative or even complementary diagnostic tools for ANA detection. The improved sensitivity of SPA technology is also changing our interpretation of the results for other types of autoantibody assays, but we need updating their calibration and new reference materials are going to be obtained in order to harmonize the assays. There is growing evidence that the identification of autoantibody combinations or profiles is helpful in improving diagnosis, patients’ subgrouping and predictivity for disease evolution in the field of SARD. We report some explanatory examples to support the idea to make the use of these autoantibody profiles more and more popular. The technological evolution of the autoimmune assays is going to change our routine diagnostic laboratory tests for SARD and validation of new algorithms is needed in order to harmonize our approach to the issue.

A comparison of a fluorescence enzyme immunoassay versus indirect immunofluorescence for initial screening of connective tissue diseases: Systematic literature review and meta-analysis of diagnostic test accuracy studies

The aim was to compare indirect immunofluorescence (IIF) and fluorescence enzyme immunoassay (FEIA) for initial screening of connective tissue diseases (CTDs) and to evaluate whether combining IIF with FEIA adds value. A comprehensive systematic literature review was conducted to identify fully paired, cross-sectional or case-control studies on ANA screening of CTD reporting results for IIF and FEIA. Study quality was assessed using the QUADAS-2 checklist. The reference standard was assessed against established classification criteria. The meta-analysis used hierarchical, bivariate and mixed-effects models to allow test results to vary within and across studies. Eighteen studies of good to fair quality were included in the review. IIF had a higher sensitivity than FEIA [cut-off 1:160, 7 studies, 3251 patients, 0.83 (95% CI 0.75-0.89) versus 0.73 (95% CI 0.64-0.80); cut-off 1:80, 7 studies, 12,311 patients, 0.89 (95% CI 0.84-0.93) versus 0.78 (95% CI 0.71-0.84)] but lower specificity [1:160, 0.81 (95% CI 0.73-0.87) versus 0.94 (95% CI 0.91-0.95); 1:80, 0.72 (95% CI 0.62-0.81) versus 0.94 (95% CI 0.90-0.96)]. A double-positive test had a higher likelihood ratio (LR) for CTD (26.2 (95% CI 23.0-29.9)) than a single positive test (14.4 (95% CI 13.1-15.9) FEIA+, 5.1 (95% CI 4.8-5.4) IIF+). A double-negative test result had more clinical value for ruling out CTD than a single negative test (LR 0.15 (95% CI 0.12-0.18) versus 0.21 (95% CI 0.18-0.25) IIF; 0.33 (95% CI 0.29-0.37) FEIA-). A FEIA+/IIF- discordant result had a higher LR than an IIF+/FEIA- discordant result (LR 2.4 (95% CI 1.7-3.4) versus 1.4 (95% CI 1.2-1.7)). Because of the comparatively higher specificity of FEIA and higher sensitivity of IIF, the combination of FEIA and IIF increases the diagnostic value. Clinicians should be acquainted with the clinical presentation of CTD and aware of the advantages and disadvantages of FEIA and IIF to avoid misinterpretation.

The clinical significance of borderline results of the Elia CTD Screen assay

Background

Data on the clinical relevance of borderline results of solid-phase assays in the screening for antinuclear antibodies (ANA) are sparse. This study aimed to determine the clinical significance of borderline results of the Elia CTD Screen (ECS; Phadia/Thermo Fisher Scientific, Freiburg, Germany), a fluoroenzymeimmunoassay incorporating 17 recombinant human nuclear antigens.

Methods

We retrospectively examined the medical records of 143 subjects with borderline ECS results for ANA-associated autoimmune disorders (AASARD) and the association with the results of indirect immunofluorescence (IIF) and confirmatory assays for ANA.

Results

AASARD were diagnosed in 10 patients (7%) with systemic lupus erythematosus (n=5; four patients were prediagnosed and in clinical remission), polymyositis overlap syndromes (n=2), scleroderma, Raynaud’s syndrome and undetermined connective tissue disease (each n=1). Most frequently, homogeneous and nucleolar IIF patterns were found. Positive ANA subsets were observed in three patients. Furthermore, four patients were diagnosed with autoimmune liver diseases and yielded positive IIF in three and positive confirmatory assays in all cases. Taken together, 129 subjects had no AASARD. Within this group, 43 patients were IIF positive and most frequently showed speckled, unspecific nucleolar and only rarely homogeneous patterns. Positive ANA subsets were found in low concentrations near to the upper reference range in 18 subjects.

Conclusions

AASARD were observed in 7% of the subjects with borderline ECS and showed homogeneous or nucleolar IIF patterns in the majority of these cases. Our findings suggest that borderline results of the ECS can be clinically relevant and support the concept of a parallel or sequential screening for ANA by both ECS and IIF.

Evaluation of an Automated Screening Assay, Compared to Indirect Immunofluorescence, an Extractable Nuclear Antigen Assay, and a Line Immunoassay in a Large Cohort of Asian Patients with Antinuclear Antibody-Associated Rheumatoid Diseases: A Multicenter Retrospective Study

We assessed the diagnostic utility of the connective tissue disease (CTD) screen as an automated screening test, in comparison with the indirect immunofluorescence (IIF), EliA extractable nuclear antigen (ENA), and line immunoassay (LIA) for patients with antinuclear antibody- (ANA-) associated rheumatoid disease (AARD). A total of 1115 serum samples from two university hospitals were assayed using these four autoantibody-based methods. The AARD group consisted of patients with systemic lupus erythematosus (SLE), systemic sclerosis (SSc), Sjögren's syndrome (SS), and mixed connective tissue disease (MCTD). The qualitative results of all four autoantibody assays showed a significant association with AARDs, compared to controls (P < 0.0001 for all). The areas under the receiver operating characteristic curves (ROC-AUCs) of the CTD screen for differentiating total AARDs, SLE, SSc, SS, and MCTD from controls were 0.89, 0.93, 0.73, 0.93, and 0.95, respectively. The ROC-AUCs of combination testing with LIA were slightly higher in patients with AARDs (0.92) than those of CTD screen alone. Multivariate analysis indicated that all four autoantibody assays could independently predict AARDs. CTD screening alone and in combination with IIF, EliA ENA, and LIA are potentially valuable diagnostic approaches for predicting AARDs. Combining CTD screen with LIA might be effective for AARD patients.

Autoantibodies Associated With Connective Tissue Diseases: What Meaning for Clinicians?

Connective tissue diseases (CTDs) such as systemic lupus erythematosus, systemic sclerosis, myositis, Sjögren's syndrome, and rheumatoid arthritis are systemic diseases which are often associated with a challenge in diagnosis. Autoantibodies (AAbs) can be detected in these diseases and help clinicians in their diagnosis. Actually, pathophysiology of these diseases is associated with the presence of antinuclear antibodies. In the last decades, many new antibodies were discovered, but their implication in pathogenesis of CTDs remains unclear. Furthermore, the classification of these AAbs is nowadays misused, as their targets can be localized outside of the nuclear compartment. Interestingly, in most cases, each antibody is associated with a specific phenotype in CTDs and therefore help in better defining either the disease subtypes or diseases activity and outcome. Because of recent progresses in their detection and in the comprehension of their pathogenesis implication in CTD-associated antibodies, clinicians should pay attention to the presence of these different AAbs to improve patient's management. In this review, we propose to focus on the different phenotypes and features associated with each autoantibody used in clinical practice in those CTDs.