The role of antineutrophil cytoplasmic antibody (c-ANCA) testing in the diagnosis of Wegener granulomatosis. A literature review and meta-analysis.

Wegener granulomatosis is a serious systemic vasculitis that is uniformly fatal if untreated. In 1983, Fauci and colleagues [1] reported their success with a combination of corticosteroid and cyclophosphamide therapy in 85 patients with Wegener granulomatosis. Since then, the recognition among clinicians of Wegener granulomatosis and its expanded clinical spectrum has improved, making early diagnosis and treatment possible. Patients with the classic Wegener triad have necrotizing granulomatous vasculitis of the upper and lower respiratory tract associated with glomerulonephritis; patients with limited Wegener granulomatosis may have vasculitis limited to the respiratory tract [2]. Because of the potential clinical overlap with other diseases, the diagnostic algorithm for patients with suspected Wegener granulomatosis has traditionally included biopsy of the upper airway, lung, or kidney to confirm the diagnosis and to rule out other entities, such as systemic infections and malignancies, that may respond adversely to cyclophosphamide therapy [3]. Antineutrophil cytoplasmic antibody (ANCA), first described in 1982 in patients with systemic vasculitis and glomerulonephritis, has emerged as a new diagnostic tool and marker of disease activity for vasculitis [4, 5]. Originally thought to be a response to arboviral infection, ANCA was later identified as a seromarker for Wegener granulomatosis [4, 6]. It is currently believed that the presence of ANCA is an important factor in the pathogenesis of this disease [5]. Two ANCA patterns may be seen with indirect immunofluorescence of ethanol-fixed neutrophils: a cytoplasmic pattern (c-ANCA) and the artifactual perinuclear pattern (p-ANCA) [7, 8]. The major antigen for c-ANCA is a 29-kd serine protease, known as proteinase 3, which is found within the azurophilic granules of the neutrophil [9]. The major antigen for p-ANCA is myeloperoxidase, a lysosomal enzyme found in neutrophils [7, 10]. Some clinical overlap has been seen, but the two patterns have different disease associations. The c-ANCA pattern has predominantly been associated with Wegener granulomatosis, and p-ANCA has been associated with microscopic polyarteritis, other vasculitides, idiopathic necrotizing and crescentic glomerulonephritis, and other diseases [7, 11-13]. Early studies of c-ANCA in patients with Wegener granulomatosis, especially those with active disease, have been promising. Reported sensitivities and specificities have exceeded 90% [10-12, 14-18]. Because of the morbidity and expense associated with biopsy, c-ANCA has attracted interest as a rapid and noninvasive way to diagnose Wegener granulomatosis. In fact, some investigators advocate immunosuppressive therapy for patients with positive c-ANCA test results and symptoms compatible with Wegener granulomatosis, even in the absence of biopsy results [19-21]. The history of c-ANCA testing appears to mirror the natural history of many new diagnostic tests. Important and early pioneering studies of new tests are typically done in highly selected patients with confirmed disease to determine the test's operating characteristics. However, when the new test is subsequently applied to unselected populations, clinical experience and additional studies often provide a less optimistic picture of its diagnostic power. Several recent reports [22-27] document false-positive c-ANCA test results in patients with tuberculosis, Hodgkin lymphoma, human immunodeficiency virus infection, nasal septal perforation, monoclonal gammopathies, and drug-induced Wegener-like disease. Similarly, additional reports [28, 29] describe negative c-ANCA test results in patients with Wegener granulomatosis, even those with active disease. Given the current enthusiasm for a serologic diagnosis of Wegener granulomatosis, underrecognition of the rate of false-positive c-ANCA test results may lead to inappropriate immunosuppressive therapy in some patients who do not have Wegener granulomatosis. Conversely, underappreciation of the frequency of false-negative c-ANCA test results may delay therapy for patients who have clinical features compatible with Wegener granulomatosis. We did a literature review and meta-analysis to assess the utility of c-ANCA as a diagnostic marker for Wegener granulomatosis overall and in relation to disease activity. Methods As noted above, two ANCA patterns have been described in the literature, and each has separate disease associations. Patients with Wegener granulomatosis often have c-ANCA, whereas p-ANCA is found in patients with various syndromes with and without vasculitis [7, 30, 31]. Because c-ANCA is thought to have a higher test sensitivity than p-ANCA for the diagnosis of Wegener granulomatosis, we focused only on c-ANCA. Search Strategy We could not determine a systematic approach for identifying unpublished data on c-ANCA, and thus we selected only published articles for our literature review. We did a MEDLINE search for English-language studies done in humans and published between 1966 and June 1993. Three searches were done: 1) a textword and registry search for antineutrophil cytoplasmic antibody [ANCA], anticytoplasmic antibody, and antineutrophil antibody; 2) a combination of search terms antibodies, neutrophils and keywords such as pulmonary-renal syndrome, or Wegener granulomatosis, or vasculitis, or glomerulonephritis; and 3) a search using the keyword pulmonary-renal syndrome alone. Using this initial search strategy, we identified 720 citations. Manual examination of the reference lists of included articles and the bibliographies of review articles and standard texts yielded an additional 27 studies, for a total of 747. Article Selection To be included in the analysis, all articles had to pass through a four-stage review (Table 1). First, the titles and abstracts of the 747 articles were independently examined by two reviewers. One reviewer was a rheumatologist, and the other was a health services researcher with a PhD who had experience in the critical appraisal of medical literature. Articles were excluded at this stage if they were not pertinent to the topic (for example, if they addressed antineutrophil antibodies and malignancy) or if they did not present patient-level data (for example, if they were reports of tissue culture experiments). If a cited article did not have a published abstract but appeared to be relevant, or if either reviewer included it, it was retained for further review. Of the original 747 articles, 407 were excluded and 340 were retained for second-level review. Table 1. Summary of the Results of Protocol for Selection of Articles for Meta-analysis In stage 2 of the review process, the complete articles were photocopied and reviewed by a rheumatologist. Articles were excluded if they were case reports (n = 64), reviews (n = 75), or letters to the editor (n = 58), or if they were irrelevant to our topic (n = 81). Sixty-two of the 340 articles remained for potential inclusion. In stage 3, a rheumatologist (JKR) and an investigator with a PhD reviewed the methods section of each article in detail. The methodologic criteria required for inclusion at this stage were specification of the patient selection method and the use of standard reference criteria to define Wegener granulomatosis. For casecontrol and cohort studies, the authors had to have described a systematic method of patient selection (for example, consecutive patients or a random sample based on prespecified criteria) [32]. Thus, case-series studies (such as those defining persons with a common feature nonsystematically without the presence of a control group) were excluded. Authors also had to specify standard reference criteria for establishing Wegener granulomatosis exclusive of the c-ANCA test result. Acceptable reference criteria included the Ear, Nose, Throat, Lung, and Kidney staging system [2], the Fauci criteria [1], and the American College of Rheumatology criteria [33]. The Ear, Nose, Throat, Lung, and Kidney system and the American College of Rheumatology criteria require biopsy confirmation of Wegener granulomatosis, and the Fauci criteria are clinicopathologic in nature. Thirty-nine articles were excluded at this stage for the following reasons: case-series design (n = 24); the method of patient selection was not clearly stated (n = 4); a reference standard was not specified (n = 7); or the article was irrelevant to our review (n = 4). If either reader included an article, it was retained for further review. In stage 4, three physicians each independently read the remaining 23 articles. Articles were excluded at this stage if a 2 2 contingency table, needed to calculate the operating characteristics, could not be constructed from the results (n = 8). Thus, 15 articles remained for detailed review [10, 11, 14, 15, 28, 34-43]. For these 15 articles, 2 2 contingency tables were constructed for patients with and without Wegener granulomatosis compared with patients with and without positive c-ANCA test results. Disagreements between reviewers were resolved by consensus. Definition of Wegener Granulomatosis We included only those studies that specified standard reference criteria for defining Wegener granulomatosis independent of the patient's c-ANCA test result [1, 2, 33]. Patients with Wegener granulomatosis can be further divided into two subtypes: those with classic and those with limited disease [2]. In classic Wegener granulomatosis, glomerulonephritis and inflammation of the upper or lower respiratory tract, or both, are present. In limited disease, the kidneys are not involved, but inflammation of the upper or lower respiratory tract, or both, is present. Only 6 of the 15 studies separated patients by subtype. Furthermore, 2 of these 6 studies did not separate the c-ANCA test results by Wegener granulomatosis subtype. Because of these inconsistencies, we considered a single classification (overall Wegener granulomatosis) to repres