Direct immunofluorescence testing in vasculitis - a single institution experience with Henoch Schönlein Purpura

Abstract

Background

Direct immunofluorescence (DIF) panels (IgG, IgA, IgM, C3 and fibrinogen) are ordered for clinically suspected vasculitis, with frequently negative results.

Methods

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 HSP. Peri/intravascular IgA was considered "positive," other reactants "non-specific," and no immunoreactivity "negative."

Results

Vasculitis was the given indication for 20% (258/1318) of DIF studies. HSP was clinically suspected in 36% (95/258). In this setting, LCV was common (66%, 63/95) and DIF was positive in 43% (27/63). 100% 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.

Conclusions

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.