Managing positive anti-glomerular basement membrane antibodies in the absence of disease

A woman in her 20s was referred to renal clinic for investigation regarding positive anti-glomerular basement membrane (anti-GBM) antibody results. Autoimmune screening was performed to investigate an episode of fever, cough and haemoptysis which presented alongside the formation of a maculopapular rash and mild proteinuria (1+) on urine reagent dipstick. Despite repeated positive anti-GBM results obtained through BioPlex 2200 multiple antibody (multiplex) immunoassay, examination four months later was unremarkable, all signs and symptoms being resolved. Urinalysis, imaging and renal function tests demonstrated no signs of disease. False positive multiplex immunoassay results were confirmed by Phadia EliA single antibody (singleplex) fluoroenzyme immunoassay, which demonstrated anti-GBM antibody levels within normal ranges. With recent positive Epstein-Barr virus serology, unspecific proteins (heterophile antibodies) made in response remain the likely false positive cause. This case highlights the risk of heterophile antibody-induced false positives in multiplex testing, heightening the risk of misdiagnosis and unnecessary intervention.