False negatives are often common with serum precipitins because of lack of testing reagents for many antigens.Precipitating IgG antibodies against fungal or avian antigens can be detected in the laboratory using the traditional Ouchterlony immunodiffusion method wherein precipitin lines form on agar plate. The ImmunoCAP technology has replaced this time-consuming, labor-intensive method with their automated CAP assays and FEIA (Fluorescence enzyme immunoassay) that can detect IgG antibodies against Aspergillus fumigatus (Farmers lung or for ABPA) or avian antigens (Bird Fanciers Lung). Differential Diagnosis
Organic dust toxic syndrome presents similarly with fevers, chills a few hours after exposure to bioaerosols with toxins from fungi, however this is not a true hypersensitivity reaction because it occurs on initial exposure without a preceding sensitization In chronic disease, HP must be differentiated from very similarly presenting idiopathic pulmonary fibrosis.Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from occupational asthma in that it is not restricted to only occupational exposure, and that asthma generally is classified as a type I hypersensitivity. Unlike asthma, hypersensitivity pneumonitis targets lung alveoli rather than bronchi.Similarly, sarcoidosis has noncaseating granuloma formation, however hilar adenopathy is often seen on chest radiographs. Treatment
The best treatment is to avoid the provoking allergen, as chronic exposure can cause permanent damage and acute disease is often self-limiting. The identification of the provoking antigen and its location must be ascertained by conducting an exposure assessment. Home cleaning is one method of antigen avoidance.
The industrial hygeinst or environmental scientist will make the decision to conduct additional sampling. Types
Hypersensitivity pneumonitis may also be called many different names, based on the provoking antigen. These include:

Of these types, Farmers Lung and Bird-Breeders Lung are the most common. "Studies document 8-540 cases per 100,000 persons per year for farmers and 6000-21,000 cases per 100,000 persons per year for pigeon breeders. High attack rates are documented in sporadic outbreaks. Prevalence varies by region, climate, and farming practices. HP affects 0.4–7% of the farming population. Reported prevalence among bird fanciers is estimated to be 20-20,000 cases per 100,000 persons at risk." Imaging
No single imaging finding is singularly definitive of a diagnosis rather clinicians rely on a constellation of findings. Both chest radiographs and high resolution CT scans can be normal. Chest Radiographs
Acute presentation may reveal poorly defined a micro-nodular interstitial pattern and ground-glass opacities in the lower and mid lung zones. In addition to this, subacute presentations may show reticular nodular opacities in mid-to-lower lung zones. Chronic forms may show fibrotic changes and appear like Idiopathic pulmonary fibrosis. High-Resolution Computed Tomography
This has become a common diagnostic imaging for the diagnosis and is the modality used in the Official ATS/JRS/ALAT Clinical Practice Guideline. Two forms of hypersensitivity pneumonitis are fibrotic and non-fibrotic findings on chest CT. The two differ in terms of their diagnostic work up and management although there is overall between them. The non-fibrotic form is typically characterized by ground glass opacities, mosaic attenuation, ill-defined centrilobular nodules (<5 mm), and air trapping.