Hypersensitivity Pneumonitis - Diagnosis - Diagnosis

To diagnose hypersensitivity pneumonitis, your doctor will collect your medical history to understand your symptoms and see if you have an exposure history to possible causative substances. Your doctor will perform a physical exam and may order diagnostic tests and procedures. Based on this information, your doctor may able to determine whether you have acute, subacute, or chronic hypersensitivity pneumonitis.

Diagnostic tests and procedures

To diagnose hypersensitivity pneumonitis, your doctor may order:

  • Blood tests to detect high levels of white blood cells and other immune cells and factors in your blood that indicate your immune system is activated and causing inflammation somewhere in your body.
  • Bronchoalveolar lavage (BAL) to collect fluid from your lungs that can be tested for high levels of white blood cells and other immune cells. High levels of these cells mean your body is making an immune response in your lungs, but low levels do not rule out hypersensitivity pneumonitis.
  • Computed tomography (CT) to image the lungs and look for inflammation or damage such as fibrosis. CT scans, particularly high-resolution ones, can help distinguish between types of hypersensitivity pneumonitis.
  • Inhalation challenge tests to see if a controlled exposure to a suspected causative substance triggers your immune system and the onset of common signs and symptoms such as an increase in temperature, increase in white blood cell levels, rales  that are heard during a physical exam, or reduced lung function. A positive test can confirm an inhaled substance triggers your immune system. A negative test does not rule out that you have hypersensitivity pneumonitis, because it may mean a different untested environmental substance is causing your condition. Before having this test, talk to your doctor about the benefits and possible risks of this procedure.
  • Lung biopsies to see if your lung tissue shows signs of inflammation, fibrosis, or other changes known to occur in hypersensitivity pneumonitis.
  • Lung function tests to see if you show signs of restriction  such as reduced breathing capacity or abnormal blood oxygen levels and check if you have obstructed airways. These tests help assess the severity of your lung disease and when repeated they can help monitor whether your condition is stable or worsening over time. Lung function tests may be normal between acute flares.
  • Precipitin tests to see if you have antibodies in your blood that recognize and bind to a causative substance. While a positive test means that you have been exposed to a substance, it cannot confirm you have hypersensitivity pneumonitis. This is because some people without this condition also have antibodies in their blood to these substances. If you have antibodies to a substance, your doctor may have you perform an inhalation challenge test to see if a new exposure to the same substance can activate your immune system and cause a new acute flare.
  • Chest x-rays to image the lungs and look for inflammation or damage such as fibrosis in your lungs.

Learn how these diagnostic tests and procedures can help distinguish between types of hypersensitivity pneumonitis.

Tell me more

Chest x-ray and CT scans, lung biopsies, and lung function tests may help your doctor diagnose the type of hypersensitivity pneumonitis that you have.

  • Chest x-rays and CT scans may show little to no inflammation in your lungs during the early phase of acute disease, but they will show obvious signs of inflammation and tissue damage such as fibrosis in subacute and chronic hypersensitivity pneumonitis.
  • Lung function tests may detect breathing difficulties, small airflow blockages, or reduced lung function in acute hypersensitivity pneumonitis. These problems may worsen and progress to severe lung restriction in subacute and chronic hypersensitivity pneumonitis.
  • Lung biopsies will reveal inflammation, fibrosis, and possibly granulomas  in subacute and chronic hypersensitivity pneumonitis. They are not usually performed for acute hypersensitivity pneumonitis.

Your medical and exposure histories can help your doctor diagnose acute hypersensitivity pneumonitis and possibly identify the substance causing your condition. This is because the exposure will have occurred right before your acute symptoms started.

Is it hard to diagnose this condition?

It can take months or even years for your doctor to diagnose hypersensitivity pneumonitis in you or your child. Learn why hypersensitivity pneumonitis can be hard to diagnose.

  • There are no clear exposure histories to potential causative substances before having symptoms. This occurs in up to 50 percent of patients who are later diagnosed with hypersensitivity pneumonitis. Despite hypersensitivity pneumonitis being a common childhood interstitial lung disease, children are often diagnosed late after the condition has progressed to chronic disease. This is because children tend to be exposed to small amounts of causative substance over long periods of time, which does not trigger obvious acute symptoms and makes it very difficult to determine their exposure history.
  • Other conditions may cause similar signs and symptoms. Before diagnosing hypersensitivity pneumonitis, your doctor must rule out: unintentional effects of medicines such as bleomycin, methotrexate, or nitrofurantoin; lung infections such as pneumonia or the flu (influenza); smoking-related lung disease; connective tissue disease; bleeding in the lungs; idiopathic pulmonary fibrosissarcoidosis; and lung cancer.
  • Diagnostic features seen in chest x-rays, CT scans, and lung biopsies may differ between children and adults. Even when a person’s exposure history is known or hypersensitivity pneumonitis is suspected, doctors look for diagnostic features in chest x-rays, CT scans, and lung biopsies that are indicators of the disease in adults. More research is needed to help map diagnostic features for children with this condition.


  • Return to Risk Factors to review family history, lifestyle, or other environmental factors that increase your risk of developing hypersensitivity pneumonitis.
  • Return to Signs, Symptoms, and Complications to review differences between acute, subacute, and chronic hypersensitivity pneumonitis.