Direct immunofluorescence testing in vasculitis-A single institution experience with Henoch-Schönlein purpura.

Abstract

Direct immunofluorescence (DIF) panels (IgG, IgA, IgM, C3 and fibrinogen) are ordered for clinically suspected vasculitis, with frequently negative results. Cases submitted for DIF and histology (2010-2014) with "vasculitis" in the clinical data were examined, and the electronic medical record reviewed for clinical suspicion of Henoch-Schönlein purpura (HSP). Peri/intravascular IgA was considered positive, other reactants non-specific and no immunoreactivity negative. Vasculitis was the given indication for 20% (258/1318) of DIF studies. HSP was clinically suspected in 36% (95/258). In this setting, leukocytoclastic vasculitis (LCV) was common (66%, 63/95) and DIF was positive in 43% (27/63). One hundred percentage of DIF+ had LCV+. In cases without HSP suspicion, 26% (42/163) were LCV+ and <1% DIF+. Of the 258 cases, LCV+ greatly enriched for DIF+ (105/258 LCV+ with 28/105 [27%] DIF+), captured 100% of HSP and included cases with non-specific DIF/etiologic findings. In LCV cases, DIF positivity was not seen, HSP was not diagnosed and non-specific DIF findings were common. LCV is an H&E-based histopathologic diagnosis that can have positive, negative and non-specific DIF results that are rarely contributory except in the setting of HSP, where DIF is best utilized with IgA as the sole immunoreactant. H&E-based triage of DIF orders is recommended.