Anti-neutrophil cytoplasmic antibodies and their clinical significance

Abstract

Anti-neutrophil cytoplasmic antibodies (ANCA) are a group of autoantibodies that cause systemic vascular inflammation by binding to target antigens of neutrophils. These autoantibodies can be found in serum from patients with systemic small-vessel vasculitis and they are considered as a biomarker for ANCA-associated vasculitis (AAV). A conventional screening test to detect ANCA in the serum is indirect immunofluorescence study, and subsequently confirmed by enzyme-linked immunosorbent assay. A positive staining of ANCA can be classified into three main categories based on the staining patterns: cytoplasmic, perinuclear, and atypical. Patients with granulomatosis with polyangiitis (GPA) mostly have a positive cytoplasmic staining pattern (c-ANCA) whilst a perinuclear pattern (p-ANCA) is more common in microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA) patients. Atypical pattern (a-ANCA) is rarely seen in patients with systemic small-vessel vasculitis but it can be found in other conditions. Here, techniques for ANCA detection, ANCA staining patterns and their clinical significances are reviewed.

Comparison between enzyme-linked immunosorbent assay and indirect immunofluorescence for detection of antineutrophil cytoplasmic antibodies

“…On the other hand, the occurrence of two negative samples in IIF with positive results for anti-PR3, an autoantibody of high clinical relevance for GPA diagnosis, suggests that anti-PR3 testing with ELISA, previously or simultaneously to the IIF test, can improve diagnostic power, as supported by previous studies. (4,6) These data show the need for revision of the current algorithm, supporting the findings of previous studies. (13,14) Our study, however, has limitations, such as the failure to evaluate the correlation between laboratory results and the clinical diagnosis of the study subjects.…”

“…(1) The group of antineutrophil cytoplasmic autoantibodies, known as ANCA, is a relevant serum marker for a group of diseases called systemic vasculites, such as granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), (2,3) in addition to having an ancillary role in the differential diagnosis of inflammatory bowel disease. (4) The classic method used by most laboratories for ANCA testing around the world is IIF with a substrate of ethanol and/or formalin-fixed human neutrophils. This test is commonly used before confirmatory testing for antigen specificities in the same laboratory where the screening was carried out, or in reference laboratories.…”

“…(1) Previous studies have shown that the specificity of IIF for ANCA testing is close to 93%, whereas sensitivity is approximately 67% to 78%, and additional tests are needed to improve this performance. (4) ELISA can play this role. (4) In this case, proteins with individual antigen specificities are used − particularly PR-3 and MPO.…”

“…(4) ELISA can play this role. (4) In this case, proteins with individual antigen specificities are used − particularly PR-3 and MPO. (1) The specific determination of anti-PR3 and anti-MPO antibodies is useful in differential diagnosis of systemic vasculites, particularly when differentiating between GPA, MPA and EGPA, which have diverse clinical presentations, prognoses and treatment responses.…”

“…(11) Although the classic method for ANCA testing is IIF followed by confirmatory ELISA, some recent studies have challenged the need for the IIF test, (12) whereas others recommend the simultaneous use of both methods which, when combined, could result in a sensitivity and specificity of 92% and 99%, respectively. (4) There is a need to revise the current diagnostic algorithm used for ANCA detection. (1,13,14) In this light, this study compared the results of the ELISA and IIF methods for ANCA testing in blood samples collected in a clinical laboratory, which is considered as a reference for this type of testing, in patients at different stages of diagnostic investigation for several suspected conditions.…”