Spirometry is a common test used to diagnose asthma, COPD (including emphysema and chronic bronchitis), cystic fibrosis, the need for a lung transplant, and other conditions that affect breathing. It is usually performed in a doctor’s office or at the hospital. Now, the development of the personal spirometer also makes it possible for people to perform their own spirometry test at home (or at school or while traveling).

Spirometry is also used to monitor how well your lungs are working once you’re being treated for a chronic lung condition.

Spirometry measures the amount (volume) and speed (flow) of air you inhale and exhale. Using these measurements help you evaluate your lung health.

The key measurements are:

FVC (Forced Vital Capacity)
The amount of air you exhale as forcefully and completely as possible after taking a deep breath. The result is measured in liters. A lower measurement may indicate less lung capacity than a normal, healthy level.
FEV1 (Forced Expiratory Volume in 1 second):
The amount of air you exhale in the first second after taking a deep breath. The result is measured in liters. A lower measurement may indicate an obstruction of your airway that keeps air from fully leaving your lungs in the first second after you exhale.
FEV1/FVC ratio
The ratio of the amount of air blown out in the first second to the total amount of air blown out. A lower measurement may indicate an obstruction of your airway that causes you to exhale less air than normal. A higher measurement may indicate a restriction of your lungs, meaning less lung capacity than a normal, healthy level.
FEF25-75 (Forced Mid-expiratory Flow)
The average speed of air flow during the middle part of your breath as you exhale. The result is measured in liters per second. A lower measurement may indicate a narrowing of your airway.
PEF (Peak Expiratory Flow):
The maximum speed of air you exhale. The result is measured in liters per second. A lower measurement may indicate a narrowing of your airway.
Flow-Volume Loop:
The speed of air you exhale measured against the amount of air you exhale.
Volume-Time Curve: The amount of air you exhale measured against time.
% Pred (% Predicted):
The result of your spirometry test compared to other healthy people of the same age, gender, height and ethnicity. This percentage determines the severity of your lung condition. The severity levels are described as follows:

  • Normal – Indicates your disease is under control
  • Mild – Indicates caution
  • Moderate – Indicates extra caution
  • Severe – Indicates a medical emergency