Spirometry FEV1/FVC Calculator

FEV1 (Forced Expiratory Volume in 1 second) is the volume of air forcefully exhaled in the first second of a maximal exhalation. FVC (Forced Vital Capacity) is the total volume of air that can be forcefully exhaled from full lung capacity. Both are measured by spirometry and are the primary lung function parameters in clinical pulmonology.

The FEV1/FVC ratio distinguishes obstructive from restrictive lung disease. A ratio below 0.70 (70%) after bronchodilator use is the GOLD criterion for diagnosing obstructive lung disease such as COPD or asthma. A normal or elevated ratio with reduced FVC suggests a restrictive pattern (such as pulmonary fibrosis). The lower limit of normal (LLN) varies by age, sex, and race.

The Global Initiative for Chronic Obstructive Lung Disease (GOLD) classifies COPD severity by post-bronchodilator FEV1 as a percentage of predicted: GOLD 1 (mild): FEV1 80% or above; GOLD 2 (moderate): FEV1 50-79%; GOLD 3 (severe): FEV1 30-49%; GOLD 4 (very severe): FEV1 below 30%. All categories require FEV1/FVC below 0.70.

Predicted values are based on regression equations derived from healthy non-smoking populations, accounting for age, sex, height, and ethnicity. The Global Lung Function Initiative (GLI) 2012 equations are now the recommended reference standard from the ERS/ATS. Spirometry values are expressed as a percentage of predicted (%pred) and as the lower limit of normal (LLN, the 5th percentile of the reference population).

Obstructive lung disease (asthma, COPD, bronchiectasis) is characterized by airflow limitation: FEV1/FVC below 0.70, reduced FEV1, and often normal or elevated FVC. Restrictive lung disease (pulmonary fibrosis, obesity, neuromuscular disease) is characterized by reduced lung volumes: normal or elevated FEV1/FVC, but reduced FVC and reduced total lung capacity (TLC). TLC below 80% predicted is required to confirm a restrictive pattern.