Diagnosing asthma can be difficult, since the symptoms are often similar to those of other respiratory conditions or heart disease. A diagnosis is usually based on a description of your symptoms, a complete medical history, a physical examination, and some laboratory tests. Diagnostic tests may include pulmonary (lung) function tests (PFTs), blood tests, chest X-rays, and allergy tests.
PFTs (pulmonary function tests) are a group of tests that are used to measure the function of the lungs. The most common PFT is a spirometry test, which uses a device called a spirometer to measure the amount and rate of air passing in and out of your airways. Another test that measures lung function is peak flow examination. This test uses a peak flow meter to measure the rate at which you breathe out air. Peak flow meters can be used at home to monitor your asthma.
Chest X-rays can be used to rule out other conditions.
Blood tests can detect elevated white blood cells, which indicate an infection. Blood tests known as arterial blood gases (ABG) can be used to measure your oxygen levels. If your doctor suspects your asthma is being triggered by allergens, blood tests can measure antibodies (IgE antibodies) to specific allergens.
Allergy skin tests may be performed along with antibody blood tests if your doctor believes your asthma symptoms are brought on by an allergen.