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Dr Harris's results1 showed that indirect immunofluorescence is a more sensitive technique than antigen specific enzyme linked immunosorbent assay (ELISA) for the diagnosis of systemic necrotising vasculitis (70% v 50%) but that ELISAs have a higher positive predictive value (87% v 76%). It was the greater sensitivity of indirect immunofluorescence that prompted the “International consensus statement on testing and reporting antineutrophil cytoplasmic antibodies (ANCA)”2 to require all laboratories to screen for ANCA by indirect immunofluorescence, but to confirm the specificity of fluorescent sera by ELISA. In our hands, adherence to the minimum requirements of the consensus statement results in a higher positive predictive value than either indirect immunofluorescence or ELISA alone (62% compared with 44% and 50%, respectively). Screening by indirect immunofluorescence has the additional advantages of being a quicker and cheaper technique than using …