Aims: To determine whether indications for ordering antineutrophil cytoplasmic antibodies (ANCA) meet the 1999 guidelines proposed for ANCA testing; and to examine the test characteristics of the ANCA test.
Methods: The indications for all ANCA tests over a two-year period were assessed and compared to the 1999 guidelines for the appropriate testing of ANCA.
Results: 1127 tests were examined. Overall 33.4% had an indication meeting the 1999 guidelines. The commonest non-guideline indications were ocular or orbital inflammation, liver disease and inflammatory bowel disease. All tests with a positive ANCA had indications for testing in line with the 1999 guidelines. In all but one case an ANCA associated small vessel vasculitis (AASVV) was present.
Conclusions: ANCA is ordered for a wide range of guideline and non-guideline indications. No cases of AASVV would have been missed if ordering were restricted to tests meeting the 1999 guidelines.
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In order to optimise the clinical utility of antineutrophil antibody (ANCA) testing for diagnosing microscopic polyangiitis, Wegener granulomatosis and isolated pauci-immune necrotising or crescentic glomerulonephritis, collectively known as the ANCA associated small vessel vasculitides (AASVV), clinical guidelines for the indications for ANCA testing were proposed in 1999.1 There is evidence that when these guidelines are not followed there is an increased false positive rate.2 Studies of ANCA test indications have shown that AASVV is not missed when testing is restricted to indications meeting the 1999 guidelines.2 3
ANCA are currently being ordered for a wide range of indications both within and outside the 1999 guidelines. This study aims to further validate the 1999 criteria by replicating previous studies and determining the appropriateness of current ANCA testing in relation to the guidelines.
All ANCA requests from Wellington Hospital inpatient and outpatient units in the two-year period from 1 January 2006 until 31 December 2007 were assessed against the 1999 guidelines.1 ANCA is tested with indirect immunofluorescence (IIF) and ELISA to identify the two most clinically important specificities of ANCA, myeloperoxidase (MPO) and proteinase 3 (PR3). Notes were examined to determine the indication for ordering ANCA. If the indication was rash, the assumption was made that it resembled cutaneous vasculitis and it was a recommended indication in the context of the 1999 guidelines. ANCA test characteristics were calculated with 95% binomial CIs.
There were 1133 tests performed between 1 January 2006 and 31 December 2007; medical records were unavailable for six patients and therefore 1127 tests were analysed.
Twenty-three patients had multiple tests, with a total of 99 ANCA tests on these 23 patients. Patient notes were reviewed, on average, 1.7 years after ANCA testing (range 0.8–2.8 years).
Overall 376 (33.4%) had indications which met the 1999 guidelines. An additional 67 tests (5.9%) were performed on patients with known AASVV. Indications for the remaining 684 (60.7%) fell outside the 1999 guidelines. Table 1 shows the breakdown.
Where indications met the 1999 guidelines, 169 tests were for glomerulonephiritis, 73 for mononeuritis multiplex or peripheral neuropathy and 58 for cutaneous vasculitis. Thirty-three were performed for pulmonary haemorrhage, 19 for longstanding sinusitis or otitis, 14 for multiple lung nodules, 7 for retro-orbital mass and 3 for subglottic tracheal stenosis. Where the 1999 guidelines were not met, the most frequent indication was ocular or orbital inflammation with 73 tests (uveitis = 57, retinal vasculitis = 6 and others = 10). All specialist groups ordered ANCA tests outside of guidelines including physicians, surgeons, psychiatrists and obstetricians (data not shown). Table 2 shows other non-guideline indications that were present on 10 or more occasions.
Overall IIF testing gave 110 positive and 18 weakly positive results. There were 17 C-ANCA (cytoplasmic) with positive PR3 ELISA and 4 P-ANCA (perinuclear) with positive MPO by ELISA. The remainder showed atypical or indeterminate patterns due to a positive ANA.
There were 50 ANCA tests requested for inflammatory bowel disease (IBD). In the 21 patients who were diagnosed with IBD during the study, only one patient had a positive ANCA by IIF (C-ANCA) and in this patient the ELISA was negative. They were subsequently diagnosed with ulcerative colitis on colonic biopsy.
Thirty ANCA tests were ordered to diagnose Churg Strauss syndrome; two had positive IIF, none of the 30 had positive ELISA. There were three diagnoses of Churg Strauss syndrome made in the study period; all had negative ANCA by IIF and ELISA.
In all but one case with positive IIF and correspondingly positive ELISA an AASVV was previously known or newly diagnosed. The exception was a C-ANCA/anti-PR3 positive patient with infective endocarditis; this patient met the 1999 guidelines by presenting with a purpuric rash. Three cases of microscopic polyangiitis were diagnosed; no Wegener granulomatosis was diagnosed in the two-year study period. In two cases renal histology was confirmatory, the other had asymmetrical peripheral neuropathy, active urinary sediment, raised inflammatory markers and a positive P-ANCA with anti-MPO ELISA. In all cases where an AASVV was diagnosed the indication for ANCA testing was either known AASVV or a 1999 guideline approved indication. Therefore no case of AASVV was diagnosed from a test ordered outside of the scope of the 1999 guidelines. Using these results the sensitivity of ANCA for diagnosing AASVV was 100.0% (95% CI 29.2% to 100.0%) and specificity was 99.9% (95% CI 99.5% to 100.0%). The positive predictive value was 75.0% (95% CI 19.4% to 99.4%) and the negative predictive value was 100.0% (95% CI 99.6% to 100.0%). ANCA tests ordered in the context of known AASVV were excluded. Only tests that were C-ANCA/anti-PR3 positive and P-ANCA/anti-MPO positive were deemed to be positive for this calculation.
The study confirmed previous research showing that a significant proportion of ANCA tests are ordered for indications outside the scope of the 1999 guidelines. There are a number of different reasons for this. The most common non-guideline indication was ocular or orbital inflammation. Uveitis made up the majority of this group. In a 140-patient case series of Wegener granulomatosis, 40 patients (29%) had ocular or orbital involvement.4 The commonest sites were orbital, scleral/episcleral and corneal. In this series uveal involvement occurred in only 4 patients (2.9% of all patients). There are reports where an AASVV was diagnosed after ANCA testing was done in the presence of otherwise idiopathic eye inflammation.5 6 All these cases manifested other indications for testing endorsed by 1999 guidelines.
The second and third most frequent non-guideline indications were liver disease and IBD. The purpose of testing in these circumstances was not to diagnose AASVV, but to diagnose IBD and immune mediated liver disease such as autoimmune hepatitis, primary biliary cirrhosis or primary sclerosing cholangitis. ANCA positivity has been described in these conditions but the test characteristics for these diseases make it unsuitable for diagnostic testing due to low sensitivity and specificity.7 8
The use of ANCA for diagnosing Churg Strauss syndrome in our study was of no clinical value, with all three cases being ANCA negative.
Studies of ANCA testing and guideline adherence have demonstrated the potential for cost saving and improvements in the clinical utility of testing with no loss of diagnostic yield.2 3 No case of AASVV was missed and in only one case over both ANCA studies, which collectively assessed 881 tests, was the diagnosis delayed, and in that case only by 2 days.3 Applying the restriction in the Sinclair et al study3 resulted in a large cost saving; applying a restriction in both the Mandl et al study2 and our study would have resulted in significant cost savings with no loss of diagnostic yield.
The retrospective nature of this study meant there was potential for error due to a lack of documentation of symptoms or signs. Therefore the number of times an ANCA test was done in accordance with the 1999 guidelines may be underestimated. Additionally the sample of tests that were analysed was not representative of all specialties.
Comparing our results to previously published studies shows that there is a significantly higher rate of non-1999 guideline appropriate ANCA tests ordered at our hospital. If the cases of known AASVV are removed, the rate of 1999 appropriate tests was 381/544 (70.0%) in the Mandl et al study2 and 171/250 (68.4%) in the Sinclair et al study.3 Our study rate of 376/1060 (35.5%) is half that of the two other published studies.
The reason for this is multifactorial, but using the test in an attempt to diagnose a condition besides AASVV makes only a small part of the disparity. A total of 547 tests were ordered in an attempt to diagnose AASVV in situations that were wholly inappropriate, including seizures, stroke, pericarditis and in fever of unknown origin. Overall lack of knowledge about the utility of the ANCA test in diagnosing both AASVV and other conditions where ANCA may be present is likely to be at the core of the disparity.
The test characteristics that we calculated are broadly in line with previous studies but have wide confidence intervals due to the small numbers.9 The one patient with a positive ANCA, without AASVV had infective endocarditis. This finding has been noted previously.10
We have shown there is poor compliance with published guidelines for ANCA testing during the study period and this result is multifactorial. Test ordering outside of the guidelines is not restricted to one specialist group. Ordering ANCA to diagnose conditions apart from AASVV is common and does not reflect the known clinical utility of the ANCA test in these situations. Applying restrictions to the ordering of ANCA in our hospital would lead to cost savings from excess additional testing. It would lead to a decrease in the time clinicians consult on patients with ANCA tests that have been ordered outside of guidelines. Applying a sustainable system for restricting inappropriate ANCA testing that is evidence based and effective is the aim of the immunology service for the future.
Antineutrophil cytoplasmic antibody (ANCA) testing should only be ordered on patients with an indication meeting the 1999 guidelines.
Failure to follow guidelines leads to increased cost and the risk of false positive results. This inevitably leads to further unnecessary testing and consultation.
Collectively studies covering over 2000 ANCA requests have demonstrated that ANCA associated small vessel vasculitis is not missed when the 1999 guidelines are followed.
The authors would like to thank Dr David Robinson for his assistance with the ANCA test database.
Competing interests: None.
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