Testing on formalin-fixed neutrophils is less sensitive and specific for small vessel vasculitis, and less sensitive for MPO-ANCA, than most ELISAs

Occurrence and Antigenic Specificity of Perinuclear Anti-Neutrophil Cytoplasmic Antibodies (P-ANCA) in Systemic Autoimmune Diseases

Perinuclear anti-neutrophilic cytoplasmic antibodies (P-ANCA) recognize heterogeneous antigens, including myeloperoxidase (MPO), lactoferrin, elastase, cathepsin-G and bactericidal/permeability-increasing protein. Although P-ANCA have diagnostic utility in vasculitides, they may also be found in patients with various other systemic autoimmune rheumatic diseases (SARDs). Nevertheless, the clinical significance and the targets recognized by P-ANCA in such patients remain unclear. For this purpose, herein we investigated the occurrence of ANCA-related antigenic specificities in 82 P-ANCA-positive sera by multiplex ELISA, as well as their association with other autoantibodies. The P-ANCA-positive sera corresponded to patients with vasculitides (n = 24), systemic lupus erythematosus (n = 28), antiphospholipid syndrome (n = 5), Sjögren’s syndrome (n = 7), rheumatoid arthritis (n = 3), systemic scleroderma (n = 1), sarcoidosis (n = 1) and Hashimoto′s thyroiditis (n = 13). In most P-ANCA-positive patients studied (51/82, 62.3%), these autoantibodies occurred in high titers (>1:160). The analysis of P-ANCA-positive sera revealed reactivity to MPO in only 50% of patients with vasculitides, whereas it was infrequent in the other disease groups studied. Reactivity to other P-ANCA-related autoantigens was also rarely detected. Our findings support that high P-ANCA titers occur in SARD. The P-ANCA-positive staining pattern is associated with MPO specificity in vasculitides, while in other autoimmune diseases, it mostly involves unknown autoantigens.

Detection of Anti-neutrophil Cytoplasmic Antibodies (ANCA) by Indirect Immunofluorescence

The eventual presence of anti-neutrophil cytoplasmic antibodies (ANCA) can initially be screened with indirect immunofluorescence (IIF). The majority of laboratories that facilitate ANCA testing use commercial kits. Although in-house assays are not encouraged in routine clinical laboratories, knowledge on the methodological aspects of the assay remains of importance. These aspects include choice of substrate, choice of fixative, staining procedure, and interpretation procedure. In this paper details on the methodology are provided and discussed in the context of the clinical application.

A dual-fixed neutrophil substrate improves interpretation of antineutrophil cytoplasmic antibodies by indirect immunofluorescence

OBJECTIVES

To determine whether the addition of a formalin-fixed neutrophil substrate could improve interpretation and prediction of autoantigenic specificity in antineutrophil cytoplasmic antibody (ANCA) testing.

METHODS

Routine diagnostic samples sent for ANCA testing were analyzed prospectively on a dual substrate of both ethanol- and formalin-fixed neutrophils. Positive samples on ethanol-fixed neutrophils were deemed "typical" if formalin-fixed neutrophils also stained, and "atypical" if not. Indirect immunofluorescence (IIF) results were correlated with antimyeloperoxidase (MPO) and anti-proteinase 3 (PR3) results with an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Of 1,426 samples, 201 from unique patients were ANCA-positive (200 on IIF, 1 on ELISA alone). Thirty-two (45%) of 71 typical ANCA staining patterns were positive for either an anti-MPO or anti-PR3 antibodies, whereas only one (0.8%) of 129 atypical patterns was ELISA-positive, in a patient without systemic vasculitis. Only one (3%) of 34 ELISA-positive samples had a negative IIF-ANCA (1/1,426 patients, 0.07%), and this patient did not have vasculitis.

CONCLUSIONS

Concomitant staining on formalin fixation of IIF-positive ethanol-fixed ANCA samples improves the interpretation of ANCA testing and is predictive of vasculitis autoantigens MPO and PR3.

Antineutrophil cytoplasm antibody: positivity and clinical correlation

OBJECTIVE

To determine positivity and clinical correlation of anti-neutrophil cytoplasmic antibodies (ANCA), taking into account the interference of antinuclear antibodies (ANA).

MATERIAL AND METHODS

A prospective study was conducted in the Laboratory of Immunology of the National Cuban Center of Medical Genetic during one year. Two hounded sixty-seven patients with indication for ANCA determination were included. ANCA and ANA determinations with different cut off points and assays were determined by indirect immunofluorescense. Anti proteinase 3 and antimyeloperoxidase antibodies were determined by ELISA.

RESULTS

Most positivity for ANCA was seen in patients with ANCA associated, primary small-vessel vasculitides, rheumatoid arthritis and systemic lupus erythematosus. Presence of ANCA without positivity for proteinase 3 and myeloperoxidase was higher in patients with ANA and little relation was observed between the perinuclear pattern confirmed in formalin and specificity by myeloperoxidase. Highest sensibility and specificity values for vasculitides diagnostic were achieved by ANCA determination using indirect immunofluorescense with a cut off 1/80 and confirming antigenic specificities with ELISA.

CONCLUSION

ANCA can be present in a great number of chronic inflammatory or autoimmune disorders in the population studied. This determination using indirect immunofluorescence and following by ELISA had a great value for vasculitis diagnosis. Anti mieloperoxidasa assay has a higher utility than the formalin assay when ANA is present.

Diagnostic value of distinguishing and reporting different perinuclear ANCA (P-ANCA) immunofluorescence patterns: a prospective study

OBJECTIVES

To investigate whether discriminating the classic perinuclear antineutrophil cytoplasmic antibody (P-ANCA) pattern from atypical P-ANCA and uninterpretable patterns improves the diagnostic utility of ANCA testing.

METHODS

All ANCA requests (n = 3,544) referred to Pathology Queensland were analyzed prospectively over 4 months for P-ANCA pattern subtypes and myeloperoxidase (MPO)-ANCA/PR3-ANCA results and correlated with clinical, laboratory, and radiologic evidence of necrotizing small vessel vasculitis.

RESULTS

Of the 436 perinuclear immunofluorescence-positive samples, 45 were classic P-ANCA, 163 were atypical P-ANCA, and 228 were antinuclear antibodies/uninterpretable. The classic P-ANCA pattern had a significantly stronger association with vasculitis (30/45) than atypical P-ANCA (2/163) (P <.0001) or ANA/uninterpretable patterns (8/228) (P <.0001). The combination of a classic P-ANCA pattern and positive MPO-ANCA/PR3-ANCA result was also more strongly associated with vasculitis than a positive MPO-ANCA/PR3-ANCA result in isolation (P = .003).

CONCLUSIONS

This study demonstrates that reporting different P-ANCA patterns (including ANA/uninterpretable patterns) provides additional diagnostic information to MPO-ANCA/PR3-ANCA results.

ANCA testing: the current stage and perspectives

During the past 30 years, remarkable progress has been achieved in understanding the role of the antineutrophil cytoplasmic antibodies (ANCAs) directed against proteinase 3 (PR3) and myeloperoxidase (MPO) in so-called "ANCA-associated vasculitides". In the right clinical context, ANCAs are a good seromarker for these diseases, have improved nomenclature of systemic vasculitides and have contributed to new pathogenic concepts. However, problems with the clinical applications of ANCA testing in daily practice remain. They can be summarised as follows: assay standardisation and performance; the use of ANCA testing in a clinical setting with a low pretest probability; the relationship between ANCA titres and disease activity remains unclear. The solution to problems regarding the ANCA diagnosis is focussed on the fundamental methods, i.e., correct implementation of IFT and ELISA, the cautious use of commercial assays and restricting the use of the tests to clinical situations with a rather high pretest probability of AAV.

Anti-neutrophil cytoplasmic autoantibodies: methodological aspects and clinical significance in systemic vasculitis

Antineutrophil cytoplasmic antibodies (ANCA) are the serological hallmark of some idiopathic systemic vasculitides, such as granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and, to a lesser extent, Churg-Strauss syndrome (CCS), the so-called ANCA-associated vasculitides (AAV). ANCA were first detected by immunofluorescence (IIFT), subsequently the target antigens myeloperoxidase (MPO) and proteinase 3 (PR3) were identified, allowing the development of the quantitative, antigen-specific assays. According to the guidelines, combining IIFT and PR3-ANCA/MPO-ANCA assures the optimal diagnostic specificity. Antigen specificity does not effectively differentiate among the different AAV, however C-ANCA/PR3-ANCA are mainly found in GPA, while P-ANCA/MPO-ANCA are more prevalent in MPA and CSS. Despite their diagnostic value, the performance of the widespread immunometric assays for ANCA testing is disappointing, particularly for the low sensitivity. In recent years, more "sensitive" assays have been developed, using the microplate as well as fully the automated technologies, with promising preliminary results. ANCA, may be detected in a number of pathological conditions other than small vessel vasculitis. However, in most of these non-vasculitic patients ANCA do not recognize MPO or PR3 as target antigens, but other granulocyte components, often multiple or unknown specificities. A positive ANCA result by itself is not diagnostic for AAV, clinical evidence and possibly histological confirmation are always required. On the other hand, a negative test result cannot completely rule out a diagnosis of AAV, as AAV without detectable ANCA exist. The appropriate use of ANCA testing strongly improves the diagnostic accuracy and clinical usefulness of the results.

Twenty-eight years with antineutrophil cytoplasmic antibodies (ANCA): how to test for ANCA - evidence-based immunology?

Wegener’s granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome, and primary pauci-immune crescentic glomerulonephritis are associated with circulating antineutrophil cytoplasmic autoantibodies (ANCA) (collectively called ANCA-associated vasculitides, AAV). Two types of ANCA, one with a cytoplasmic fluorescence pattern (C-ANCA) and specificity for proteinase 3 (PR3-ANCA) and the other with a perinuclear pattern (P-ANCA) and specificity for myeloperoxidase (MPO-ANCA), account for this association and are highly specific markers for these vasculitides. AAV most often require therapy with cytotoxic and antiinflammatory agents, and hence a well-established diagnosis is mandatory to avoid unnecessary and risky treatment. The widespread use of ANCA screening in the past decade has resulted in the occurrence of greater numbers of false-positive results and has led to greater difficulty in test interpretation. Methods for ANCA detection have been standardized internationally in large multicentre studies and an international consensus statement on testing and reporting of ANCA has been pub lished (1999 and 2003). Despite these advances, problems with the extended use of ANCA testing in daily clinical practice remain. They may be summarized as follows: (1) the basic standards for ANCA testing are not uniformly met; (2) there is still controversy over the value of formalin fixation of neutrophils in differentiating P-ANCA from antinuclear antibodies (what is the place of this substrate in ANCA testing?); (3) the new generation of PR3-ANCA and MPO-ANCA ELISAs are more sensitive and specific than immunofluorescence testing (should ELISAs replace the immunofluorescence test?); and (4) should alternative methods for ANCA detection such as image analysis and/or multiplex immunoassays be used for screening? In this paper, we review these issues, identify areas of uncertainty, and provide practical guidelines where possible.

Laboratory investigation in the diagnosis of vasculitis

Few tests have been firmly established to diagnose primary systemic vasculitides. Although antineutrophil cytoplasmic autoantibodies (ANCA) are an exception, no consensus exists on the best method to detect them and they have proved of limited aid in relapse prediction. This article discusses common methods and techniques used to detect ANCA, their clinical usefulness, and recent biomarkers that may replace ANCA in established disease.