Page 178 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

154 Elena Csernok

Introduction

In 1982, Davies and colleagues [1] discovered the association of the antineutrophil
antibody in segmental necrotizing glomerulonephritis, and three years later, Van der Woude
and coworkers [2] characterized their presence as a diagnostic tool and marker of disease in
Wegener?s granulomatosis. The spectrum of diseases associated with antineutrophil
cytoplasmic antibodies (ANCA) has since increased. Two ANCA are highly associated
markers for ANCA-associated vasculitides (AAV), the latter of which includes
granulomatosis with polyangiitis (GPA, [Wegener`s]), microscopic polyangiitis (MPA),
eosinophil granulomatosis with polyangiitis (EGPA), and primary pauci-immune crescentic
glomerulonephritis, namely C-ANCA synonymous with cytoplasmic fluorescence and
specificity for proteinase 3 (PR3-ANCA) and P-ANCA with perinuclear fluorescence and
specificity for myeloperoxidase. However, low titer ANCA can be demonstrated in patients
with inflammatory disease due to irritable bowel disease (IBD), autoimmune liver disease,
rheumatoid arthritis (RA), and drug-induced vasculitides, often with multiple antigen
specificities and unclear clinical significance. Despite efforts to the contrary, controversies
and uncertainties in ANCA testing still exist in daily clinical practice notably with respect to
lack of standardization, the inclusion of new generations of more sensitive, specific and faster
PR3- and MPO-ANCA enzyme linked immunosorbent assays (ELISA) to replace standard
immunofluorescence tests (IFT), the need for screening algorithm including clinical gating
policies to guide the flow of studies in most diagnostic laboratories. This chapter considers
current data on ANCA testing, the application of particular ANCA assays, and how such
testing can be used in the management of patients with small-vessel vasculitis.

ANCA Testing in Small-Vessel Vasculitis

An international consensus statement [4] provided guidelines for ANCA testing and
recommended screening for by IFT and mandatory antigen-specific ELISA for positive IFT
tests [4, 5]. The three major patterns demonstrated with IFT (Figure 1). The first is granular
cytoplasmic neutrophil fluorescence with central interlobular accentuation (“C-ANCA”) so
noted overall in 90% of patients, in particular in active generalized GPA. The second is
perinuclear neutrophil staining often with nuclear extension (“P-ANCA”) so noted in those
with MPA and EGPA. So called “atypical” patterns are infrequent, comprising a mix of
cytoplasmic and perinuclear fluorescence, with multiple antigen specificities; such diversity
can be encountered in association with drug exposure, IBD and RA, most often in the absence
of vasculitis [3].

There are significant differences in sensitivity, specificity and predictive value among
commercially-available ANCA ELISA kits. The sensitivity of capture as well anchor ELISA
is superior to conventional ELISA and IFT [6, 7].

Conventional ELISA using PR3 directly immobilized to the surface of the ELISA plate
shows considerable variation in performance and often lacks sensitivity. The capture ELISA
technique reduces the covering of possible epitopes by the plastic plate so noted in
conventional ELISA and demonstrates overall superiority in diagnostic performance.

Complimentary Contributor Copy