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Laboratory imposed restrictions on ANCA testing

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Testing for antineutrophil cytoplasmic antibodies (ANCA) is useful for patients with Wegener’s granulomatosis or other systemic vasculitides. When laboratories accede to all requests for ANCA testing however, the results may be difficult to interpret or irrelevant because more than half of positive tests are in patients who do not have a systemic vasculitis. In Portsmouth, UK a policy of selective testing has been in place for ten years and has resulted in more focused requesting of ANCA tests by clinicians.

The laboratory has performed ANCA testing only when the request form indicated one of the following conditions; acute or chronic renal failure, polyarteritis nodosa, Wegener’s granulomatosis (established or suspected), proteinuria or haematuria (requests from the renal/transplant unit), Churg-Strauss syndrome, nephrotic syndrome, abnormality on chest x ray or lung biopsy, haemoptysis, perforation of the nasal septum, or Henoch-Schonlein purpura. (Scleritis, prolonged sinusitis, and sudden hearing loss have recently been added to the list.) Requests not conforming to this list are refused initially but can be discussed. During the six months of June to January 2000 there were 287 requests for ANCA testing. Two hundred and eight (72.5%) were regarded as appropriate and 75 were refused. (Four requests made in person by a consultant were allowed although they would not otherwise have been regarded as appropriate.) In 1991–2, before the introduction of selection, 508 ANCA tests were done and the total number of routine autoimmunity tests (including rheumatoid factor, antinuclear, antithyroid, anti-endomysium, antismooth muscle, antimitochondrial, anticardiolipin, and antidouble stranded DNA antibodies) was 12068 (4.2% ANCA). In 2002–3 there were 930 ANCA requests out of a total of 38543 (2.4%). The calculated saving in laboratory costs was £2000 per year.

Two years after the end of the study all laboratory data subsequently accumulated for the 287 study patients was reviewed. Among the 75 patients who had ANCA testing requested but not performed only one patient had had a diagnosis of systemic vasculitis (Wegener’s granulomatosis). Her ANCA testing had been delayed by only two days however, because a second sample had been sent with the information, “episcleritis/haematuria and proteinuria”. Of the 212 ANCA tests done 57 (27%) were positive, 37 for cytoplasmic ANCA and 20 for perinuclear ANCA. Forty two of the 57 patients proved to have an ANCA related vasculitis (43 Wegener’s, five microscopic polyangiitis, and two Goodpasture’s).

Since the introduction of the selective policy there have been fewer ‘inappropriate’ requests for ANCA testing. Clinicians have been ‘educated’ (but the renal/transplant unit was apparently a major source of requests and one of the three authors of this paper was a consultant renal physician). The authors maintain that their policy makes testing more efficient and clinically relevant as well as saving money.