Pulmonary-renal syndrome: when clinical findings guide laboratory testing

Abstract

In case of ANCA vasculitis, ANCA can be detected primarily in two ways : through indirect immunofluorescence (IIF) on fixed neutrophils to identify perinuclear (P-ANCA) or cytoplasmic (C-ANCA) fluorescence, and through immunoassays such as Enzyme-Linked ImmunoSorbent Assay (ELISA) to detect antibodies targeting proteinase 3 (PR3) or myeloperoxidase (MPO). IIF was the only technique available until the introduction of commercial ELISA tests in 1990. Now, the sensitivity and specificity of modern immunoassays detecting anti-PR3 and anti-MPO antibodies surpass those of IIF. As a result, many laboratories have changed their current practice : if ANCA vasculitis is suspected, the search for anti-PR3 and anti-MPO antibodies is preferred. IIF is reserved to confirm a positive result. However, when the ELISA test is negative, yet clinical suspicion of vasculitis remains high, IIF is still recommended. So, IIF and ELISA are two complementary diagnostic tools that should be interpreted within the clinical context. ANCA vasculitis is characterized by its heterogeneous clinical presentation. Confirmation by tissue biopsy is generally warranted. Compared with other organs, kidney biopsy is preferred due to its high diagnostic yield and the ability to quantify the severity of the lesion. Severe organ damage or life-threatening conditions determine the type of treatment.