How to read pulmonary function test results

Written by steven lacher
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How to read pulmonary function test results
Pulmonary function tests measure the health and capacity of your lungs. (beautiful doctor image by sasha from

A pulmonary function test, or a spirometry test, is used to evaluate your lungs' airflow and capacity. During the test, you breathe into a device called a spirometer in a variety of ways, including both forced and rapid breathing. The spirometer records the rate and amount of air you breathe. Spirometry tests are used to diagnose lung disease, assess response to medication, and measure how contaminant exposure may affect lung function. Results are compared to a series of predicted values based on your age, gender, height, weight and ethnicity, and are expressed as a percentage of those values.

Skill level:


  1. 1

    Review your test for your forced vital capacity, or FVC, results. FVC is a measurement of the volume that can be forcefully exhaled after maximum inhalation. A normal FVC reading is generally 85 per cent of the predicted value. A smaller FVC can be indicative of an obstructive disease, which causes a smaller amount of air to be expended over time. It also may indicate a restrictive lung disease, which limits the volume of air that can be exhaled.

  2. 2

    Review your test for your FEV1 result. FEV1 stands for "forced expiratory volume in one second." It measures the volume of the air that can be forcibly exhaled in the first second of a full, forcible exhale. FEV1 is measured in litres. A normal FEV1 reading is generally 85 per cent of the predicted value. A low FEV1 is often indicative of obstructive diseases such as asthma or emphysema.

  3. 3

    Review your test for your FVC/FEV1 ratio result. This reading is used to distinguish between obstructive and restrictive lung diseases. Low FVC alone is indicative of obstructive disease, whereas the combination of a low FVC and low FEV1 is indicative of a restrictive disease.

Tips and warnings

  • The severity of lung dysfunction is based on the degree of deviation from predicted results. Mild dysfunction is between 60 per cent and 79 per cent of predicted results; moderate dysfunction is between 40 per cent and 59 per cent; and severe dysfunction is below 40 per cent.
  • Test results are highly dependent on a patient's compliance with instructions given during the test. It is not uncommon for a patient's emotional state to dramatically effect test results.

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