This is a good way to help exclude other similar lung diseases like sarcoidosis, infection and Idiopathic pulmonary fibrosis. Lung biopsy
Lung biopsies can be diagnostic in cases of chronic hypersensitivity pneumonitis, or may help to suggest the diagnosis and trigger or intensify the search for an allergen. The main feature of chronic hypersensitivity pneumonitis on lung biopsies is expansion of the interstitium by lymphocytes accompanied by an occasional multinucleated giant cell or loose granuloma.When fibrosis develops in chronic hypersensitivity pneumonitis, the differential diagnosis in lung biopsies includes the idiopathic interstitial pneumonias. This group of diseases includes usual interstitial pneumonia, non-specific interstitial pneumonia and cryptogenic organizing pneumonia, among others.The prognosis of some idiopathic interstitial pneumonias, e.g. idiopathic usual interstitial pneumonia (i.e. idiopathic pulmonary fibrosis), are very poor and the treatments of little help. This contrasts the prognosis (and treatment) for hypersensitivity pneumonitis, which is generally fairly good if the allergen is identified and exposures to it significantly reduced or eliminated. Thus, a lung biopsy, in some cases, may make a decisive difference. Serum Precipitins
Assays for serum IgGs can aid in identifying possible antigenic exposures and are used as markers of exposure  However, there use is limited in making a definitive diagnosis because serum antibody levels are often elevated in those people who are exposed to an antigen but do not have the disease. Up to 90% of people exposed to the antigen have precipitins but only 50% of similarly exposed people who are asymptomatic have the same precipitins.
δ-Aminolevulinic acid (also dALA, δ-ALA, 5ALA or 5-aminolevulinic acid), an endogenous non-proteinogenic amino acid, is the first compound in the porphyrin synthesis pathway, the pathway that leads to heme in mammals, as well as chlorophyll in plants. 5ALA is used in photodynamic detection and surgery of cancer. Medical uses
As a precursor of a photosensitizer, 5ALA is also used as an add-on agent for photodynamic therapy. In contrast to larger photosensitizer molecules, it is predicted by computer simulations to be able to penetrate tumor cell membranes. Cancer diagnosis
Photodynamic detection is the use of photosensitive drugs with a light source of the right wavelength for the detection of cancer,  using fluorescence of the drug. 5ALA, or derivatives thereof, can be used to visualize bladder cancer by fluorescence imaging. Cancer treatment
Aminolevulinic acid is being studied for photodynamic therapy (PDT) in a number of types of cancer. It is not currently a first line treatment for Barretts esophagus. Its use in brain cancer is currently experimental. It has been studied in a number of gynecological cancers.Aminolevulinic acid is indicated in adults for visualization of malignant tissue during surgery for malignant glioma (World Health Organization grade III and IV). It is used to visualise tumorous tissue in neurosurgical procedures. Studies since 2006 have shown that the intraoperative use of this guiding method may reduce the tumour residual volume and prolong progression-free survival in people with malignant gliomas. The US FDA approved aminolevulinic acid hydrochloride (ALA HCL) for this use in 2017.