A FEV1/FEVC ratio less than _____________% is significant for obstructive lung disease.

The FEV1/FEVC ratio is a crucial parameter in evaluating lung function, particularly in differentiating between obstructive and restrictive lung diseases. FEV1 (Forced Expiratory Volume in one second) measures how much air a person can forcefully exhale in one second, while FEVF (Forced Vital Capacity) measures the total amount of air exhaled during a forced expiration.

A FEV1/FEVC ratio of less than 70% is generally used as a standard threshold for diagnosing obstructive lung disease. However, a value below 80% can indicate significant obstruction in some clinical settings and populations, leading to the preference for this higher cutoff in some assessments.

In this context, a ratio lower than 80% indicates that the FEV1 is significantly reduced relative to the total forced vital capacity, which reveals the air trapping and expiratory flow limitation that characterizes obstructive conditions such as asthma or chronic obstructive pulmonary disease (COPD). This distinction is important for proper diagnosis and management of respiratory diseases.