• Vol. 48 No. 1
  • 15 January 2019

Specific Serum Immunoglobulin G (IgG) Levels Against Antigens Implicated in Hypersensitivity Pneumonitis in Asymptomatic Individuals

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Hypersensitivity pneumonitis (HP) is a complex syndrome
resulting from repeated exposure to a variety of organic
particles. It was previously thought to be uncommon, with
an incidence of 0.9 per 100,000 person-years,1 but a recent
retrospective case-cohort study demonstrated that in a
population of patients initially diagnosed with idiopathic
pulmonary fibrosis, up to 43% may be reclassified as HP.2
This highlights the challenges in making a diagnosis of HP
in patients who have presented with an undifferentiated
interstitial lung disease, particularly when the clinical
history of allergen exposure cannot be elicited. There is
currently no universally agreed upon diagnostic criteria for
HP. Vasoka et al has proposed a novel classification system
and diagnostic algorithm wherein the diagnosis of HP may
be made confidently if there is positive exposure history
to a known allergen along with typical radiological and
bronchoalveolar lavage findings. In the setting of negative
or uncertain history of exposure to a known allergen,
serum specific immunoglobulin G (IgG) may be used as a
surrogate for said exposure history to support a diagnosis
of probable or possible HP.

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