Background noise of infection for using ANCA as a diagnostic tool for vasculitis in tropical and developing countries.

Antineutrophil cytoplasmic antibody (ANCA) is often used in the laboratory to confirm paucicellular vasculitis like Wegener's granulomatosis, Churg Strauss syndrome or polyarteritis nodosa in the presence of suggestive clinical features. In tropical countries, tuberculosis, leprosy and, occasionally, malaria can produce clinical features similar to a vasculitic illness and all the three infections are known to be associated with auto antibodies. We tested 318 patients suffering from malaria, tuberculosis or leprosy for ANCA positivity. ANCA positivity was found in 19%, 32% and 30% of malaria, tuberculosis and leprosy patients (Pradhan V, Badakere S, Shankarkumar V, Iyer Y, Ghosh K, Karnad D, Indian J Malariol, 39:51-59, 2002; Pradhan V, Badakere S, Ghosh K, Pawar A, Indian J Med Sci, 58:283-288, 2004a; Pradhan V, Badakere S, Shankarkumar V, Lepr Rev, 75:50-56, 2004b), respectively, raising the possibility that ANCA positivity with clinical features suggestive of vasculitis in tropical countries may even be related to the background noise of this seropositivity caused by one of these three infections rather than confirming the diagnosis of paucicellular vasculitis. Hence, one should be careful about the background noise of ANCA positivity caused by these infections while diagnosing a vasculitic illness.