This is a medical question of type : exams and tests 
 How to diagnose Hypersensitivity Pneumonitis ? 
 To diagnose hypersensitivity pneumonitis (HP), your doctor must pinpoint the antigen that's causing the disease and its source. (An antigen is a substance that your body reacts against, such as molds, dusts, and chemicals.)
                
Your doctor will ask you detailed questions about:
                
Your current and past jobs
                
Your hobbies and leisure activities
                
The types of places where you spend time
                
Your exposure to damp and moldy places
                
Your doctor also will do a physical exam and look at test results to diagnose HP.
                
Physical Exam
                
During the physical exam, your doctor will ask about your signs and symptoms, such as coughing and weight loss. Your doctor also will look for signs of HP. For example, he or she will listen to your lungs with a stethoscope for abnormal breathing sounds. HP can cause a crackling sound when you breathe.
                
Your doctor also may look for signs of pulmonary fibrosis, a possible complication of chronic (ongoing) HP. Pulmonary fibrosis is a condition in which tissue deep in your lungs becomes scarred over time.
                
Your doctor also may check for clubbing. Clubbing is the widening and rounding of the tips of the fingers or toes. A low level of oxygen in the blood causes this condition.
                
Diagnostic Tests and Procedures
                
To help diagnose HP, your doctor may recommend or more of the following tests or procedures.
                
Chest X Ray or Chest Computed Tomography (CT) Scan
                
A chest x ray and chest CT scan create pictures of the structures inside your chest, such as your heart, lungs, and blood vessels. These pictures can show signs of HP.
                
Lung Function Tests
                
Lung function tests measure how much air you can breathe in and out, how fast you can breathe air out, and how well your lungs can deliver oxygen to your blood. One of these tests is spirometry (spi-ROM-eh-tre).
                
During this test, a technician will ask you to take a deep breath. Then, you'll blow as hard as you can into a tube connected to a small machine. The machine is called a spirometer. The machine measures how much air you breathe out. It also measures how fast you can blow air out.
                
Pulse Oximetry
                
This test measures the amount of oxygen in your blood. A small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood.
                
Precipitin Test
                
This blood test looks for antibodies (proteins) that your body creates in response to antigens. The presence of these proteins may suggest HP.
                
Challenge Test
                
During this test, you're re-exposed to the suspected antigen. Then, you'll be watched for signs and symptoms of HP.
                
Bronchoscopy
                
For bronchoscopy (bron-KOS-ko-pee), your doctor passes a thin, flexible tube through your nose (or sometimes your mouth), down your throat, and into your airways. At the tip of the tube are a light and mini-camera. This allows your doctor to see your windpipe and airways.
                
Your doctor may insert forceps (a device used to grab or hold things) through the tube to collect a tissue sample. You'll be given medicine to make you relaxed and sleepy during the procedure.
                
Bronchoalveolar Lavage
                
During bronchoscopy, your doctor may inject a small amount of salt water (saline) through the tube into your lungs. This method is called bronchoalveolar lavage (BRONG-ko-al-VE-o-lar lah-VAHZH).
                
This fluid washes the lungs and helps bring up cells from the airways and the area around the air sacs. Your doctor will look at these cells under a microscope.
                
Surgical Lung Biopsy
                
To confirm a diagnosis of HP, your doctor may do a surgical lung biopsy. Your doctor can use a biopsy to rule out other causes of symptoms and check the condition of your lungs.
                
For a surgical lung biopsy, your doctor takes samples of lung tissue from several places in your lungs. He or she then looks at them under a microscope. Your doctor may use one of the following methods to get lung tissue samples.
                
Video-assisted thoracoscopy (thor-ah-KOS-ko-pee). For this procedure, your doctor inserts a small, lighted tube with a camera (endoscope) into your chest through small cuts between your ribs.
                
The endoscope provides a video image of your lungs and allows your doctor to collect tissue samples. This procedure is done in a hospital. You'll be given medicine to help you sleep through the procedure.
                
Thoracotomy (thor-ah-KOT-o-me). For this procedure, your doctor removes a few small pieces of lung tissue through a cut in the chest wall between your ribs. Thoracotomy is done in a hospital. You'll be given medicine to help you sleep through the procedure.